Re: [PATCH v5 03/23] PCI: hotplug: Add a flag for the movable BARs feature
On Wed, Oct 16, 2019 at 06:50:30PM +0300, Sergey Miroshnichenko wrote:
> On 10/16/19 1:14 AM, Bjorn Helgaas wrote:
> > On Mon, Sep 30, 2019 at 03:59:25PM +0300, Sergey Miroshnichenko wrote:
> > > On 9/28/19 1:02 AM, Bjorn Helgaas wrote:
> > > > It's possible that a hot-add will trigger this attempt to move things
> > > > around, and it's possible that we won't find space for the new device
> > > > even if we move things around. But are we certain that every device
> > > > that worked *before* the hot-add will still work *afterwards*?
> > > >
> > > > Much of the assignment was probably done by the BIOS using different
> > > > algorithms than Linux has, so I think there's some chance that the
> > > > BIOS did a better job and if we lose that BIOS assignment, we might
> > > > not be able to recreate it.
> > >
> > > If a hardware has some special constraints on BAR assignment that the
> > > kernel is not aware of yet, the movable BARs may break things after a
> > > hotplug event. So the feature must be disabled there (manually) until
> > > the kernel get support for that special needs.
> >
> > I'm not talking about special constraints on BAR assignment. (I'm not
> > sure what those constraints would be -- AFAIK the constraints for a
> > spec-compliant device are all discoverable via the BAR size and type
> > (or the Enhanced Allocation capability)).
> >
> > What I'm concerned about is the case where we boot with a working
> > assignment, we hot-add a device, we move things around to try to
> > accommodate the new device, and not only do we fail to find resources
> > for the new device, we also fail to find a working assignment for the
> > devices that were present at boot. We've moved things around from
> > what BIOS did, and since we use a different algorithm than the BIOS,
> > there's no guarantee that we'll be able to find the assignment BIOS
> > did.
>
> If BAR assignment fails with a hot-added device, these patches will
> disable BARs for this device and retry, falling back to the situation
> where number of BARs and their size are the same as they were before
> the hotplug event.
>
> If all the BARs are immovable - they will just remain on their
> positions. Nothing to break here I guess.
>
> If almost all the BARs are immovable and there is one movable BAR,
> after releasing the bridge windows there will be a free gap - right
> where this movable BAR was. These patches are keeping the size of
> released BARs, not requesting the size from the devices again - so the
> device can't ask for a larger BAR. The space reserving is disabled by
> this patchset, so the kernel will request the same size for the bridge
> window containing this movable BAR. So there always will be a gap for
> this BAR - in the same location it was before.
>
> Based on these considerations I assume that the kernel is always able
> to arrange BARs from scratch if a BIOS was able to make it before.
>
> But! There is an implicit speculation that there will be the same
> amount of BARs after the fallback (which is equivalent to a PCI rescan
> triggered on unchanged topology). And two week ago I've found that
> this is not always true!
>
> I was testing on a "new" x86_64 PC, where BIOS doesn't reserve a space
> for SR-IOV BARs (of a network adapter). On the boot, the kernel wasn't
> arranging BARs itself - it took values written by the BIOS. And the
> bridge window was "jammed" between immovable BARs, so it can't expand.
> BARs of this device are also immovable, so the bridge window can't be
> moved away. During the PCI rescan, the kernel tried to allocate both
> "regular" and SR-IOV BARs - and failed. Even without changes in the
> PCI topology.
>
> So in the next version of this series there will be one more patch,
> that allows the kernel to ignore BIOS's setting for the "safe" (non-IO
> and non-VGA) BARs, so these BARs will be arranged kernel-way - and
> also those forgotten by the BIOS.
This still seems a little scary, so I'll probably ask about it again :)
> After modifying the code as you advised, it became possible to mark
> only some BARs of the device as immovable. So the code is less ugly
> now, and it also works for drivers/video/fbdev/efifb.c , which uses
> the BAR in a weird way (dev->driver is NULL, but not the res->child):
>
> static bool pci_dev_movable(struct pci_dev *dev,
> bool res_has_children)
> {
> if (!pci_can_move_bars)
> return false;
>
> if (dev->driver && dev->driver->rescan_prepare)
> return true;
>
> if (!dev->driver && !res_has_children)
> return true;
>
> return false;
> }
>
> bool pci_dev_bar_movable(struct pci_dev *dev, struct resource *res)
> {
> if (res->flags & IORESOURCE_PCI_FIXED)
> return false;
>
> #ifdef CONFIG_X86
> /* Workaround for the legacy VGA memory 0xa-0xb */
> if (res->start == 0xa)
Nit here; "res->start" is the CPU address, but what you need to check
is the
Re: [PATCH v5 03/23] PCI: hotplug: Add a flag for the movable BARs feature
On 10/16/19 1:14 AM, Bjorn Helgaas wrote: On Mon, Sep 30, 2019 at 03:59:25PM +0300, Sergey Miroshnichenko wrote: Hello Bjorn, On 9/28/19 1:02 AM, Bjorn Helgaas wrote: On Fri, Aug 16, 2019 at 07:50:41PM +0300, Sergey Miroshnichenko wrote: When hot-adding a device, the bridge may have windows not big enough (or fragmented too much) for newly requested BARs to fit in. And expanding these bridge windows may be impossible because blocked by "neighboring" BARs and bridge windows. Still, it may be possible to allocate a memory region for new BARs with the following procedure: 1) notify all the drivers which support movable BARs to pause and release the BARs; the rest of the drivers are guaranteed that their devices will not get BARs moved; 2) release all the bridge windows except of root bridges; 3) try to recalculate new bridge windows that will fit all the BAR types: - fixed; - immovable; - movable; - newly requested by hot-added devices; 4) if the previous step fails, disable BARs for one of the hot-added devices and retry from step 3; 5) notify the drivers, so they remap BARs and resume. You don't do the actual recalculation in *this* patch, but since you mention the procedure here, are we confident that we never make things worse? It's possible that a hot-add will trigger this attempt to move things around, and it's possible that we won't find space for the new device even if we move things around. But are we certain that every device that worked *before* the hot-add will still work *afterwards*? Much of the assignment was probably done by the BIOS using different algorithms than Linux has, so I think there's some chance that the BIOS did a better job and if we lose that BIOS assignment, we might not be able to recreate it. If a hardware has some special constraints on BAR assignment that the kernel is not aware of yet, the movable BARs may break things after a hotplug event. So the feature must be disabled there (manually) until the kernel get support for that special needs. I'm not talking about special constraints on BAR assignment. (I'm not sure what those constraints would be -- AFAIK the constraints for a spec-compliant device are all discoverable via the BAR size and type (or the Enhanced Allocation capability)). What I'm concerned about is the case where we boot with a working assignment, we hot-add a device, we move things around to try to accommodate the new device, and not only do we fail to find resources for the new device, we also fail to find a working assignment for the devices that were present at boot. We've moved things around from what BIOS did, and since we use a different algorithm than the BIOS, there's no guarantee that we'll be able to find the assignment BIOS did. If BAR assignment fails with a hot-added device, these patches will disable BARs for this device and retry, falling back to the situation where number of BARs and their size are the same as they were before the hotplug event. If all the BARs are immovable - they will just remain on their positions. Nothing to break here I guess. If almost all the BARs are immovable and there is one movable BAR, after releasing the bridge windows there will be a free gap - right where this movable BAR was. These patches are keeping the size of released BARs, not requesting the size from the devices again - so the device can't ask for a larger BAR. The space reserving is disabled by this patchset, so the kernel will request the same size for the bridge window containing this movable BAR. So there always will be a gap for this BAR - in the same location it was before. Based on these considerations I assume that the kernel is always able to arrange BARs from scratch if a BIOS was able to make it before. But! There is an implicit speculation that there will be the same amount of BARs after the fallback (which is equivalent to a PCI rescan triggered on unchanged topology). And two week ago I've found that this is not always true! I was testing on a "new" x86_64 PC, where BIOS doesn't reserve a space for SR-IOV BARs (of a network adapter). On the boot, the kernel wasn't arranging BARs itself - it took values written by the BIOS. And the bridge window was "jammed" between immovable BARs, so it can't expand. BARs of this device are also immovable, so the bridge window can't be moved away. During the PCI rescan, the kernel tried to allocate both "regular" and SR-IOV BARs - and failed. Even without changes in the PCI topology. So in the next version of this series there will be one more patch, that allows the kernel to ignore BIOS's setting for the "safe" (non-IO and non-VGA) BARs, so these BARs will be arranged kernel-way - and also those forgotten by the BIOS. I'm not sure why the PCI_CLASS_DISPLAY_VGA special case is there; can you add a comment about why that's needed? Obviously we can't move the 0xa legacy frame buffer because I think devices are allowed to claim that
Re: [PATCH v5 03/23] PCI: hotplug: Add a flag for the movable BARs feature
On Mon, Sep 30, 2019 at 03:59:25PM +0300, Sergey Miroshnichenko wrote: > Hello Bjorn, > > On 9/28/19 1:02 AM, Bjorn Helgaas wrote: > > On Fri, Aug 16, 2019 at 07:50:41PM +0300, Sergey Miroshnichenko wrote: > > > When hot-adding a device, the bridge may have windows not big enough (or > > > fragmented too much) for newly requested BARs to fit in. And expanding > > > these bridge windows may be impossible because blocked by "neighboring" > > > BARs and bridge windows. > > > > > > Still, it may be possible to allocate a memory region for new BARs with > > > the > > > following procedure: > > > > > > 1) notify all the drivers which support movable BARs to pause and release > > > the BARs; the rest of the drivers are guaranteed that their devices > > > will > > > not get BARs moved; > > > > > > 2) release all the bridge windows except of root bridges; > > > > > > 3) try to recalculate new bridge windows that will fit all the BAR types: > > > - fixed; > > > - immovable; > > > - movable; > > > - newly requested by hot-added devices; > > > > > > 4) if the previous step fails, disable BARs for one of the hot-added > > > devices and retry from step 3; > > > > > > 5) notify the drivers, so they remap BARs and resume. > > > > You don't do the actual recalculation in *this* patch, but since you > > mention the procedure here, are we confident that we never make things > > worse? > > > > It's possible that a hot-add will trigger this attempt to move things > > around, and it's possible that we won't find space for the new device > > even if we move things around. But are we certain that every device > > that worked *before* the hot-add will still work *afterwards*? > > > > Much of the assignment was probably done by the BIOS using different > > algorithms than Linux has, so I think there's some chance that the > > BIOS did a better job and if we lose that BIOS assignment, we might > > not be able to recreate it. > > If a hardware has some special constraints on BAR assignment that the > kernel is not aware of yet, the movable BARs may break things after a > hotplug event. So the feature must be disabled there (manually) until > the kernel get support for that special needs. I'm not talking about special constraints on BAR assignment. (I'm not sure what those constraints would be -- AFAIK the constraints for a spec-compliant device are all discoverable via the BAR size and type (or the Enhanced Allocation capability)). What I'm concerned about is the case where we boot with a working assignment, we hot-add a device, we move things around to try to accommodate the new device, and not only do we fail to find resources for the new device, we also fail to find a working assignment for the devices that were present at boot. We've moved things around from what BIOS did, and since we use a different algorithm than the BIOS, there's no guarantee that we'll be able to find the assignment BIOS did. > > I'm not sure why the PCI_CLASS_DISPLAY_VGA special case is there; can > > you add a comment about why that's needed? Obviously we can't move > > the 0xa legacy frame buffer because I think devices are allowed to > > claim that region even if no BAR describes it. But I would think > > *other* BARs of VGA devices could be movable. > > Sure, I'll add a comment to the code. > > The issue that we are avoiding by that is the "nomodeset" command line > argument, which prevents a video driver from being bound, so the BARs > are seems to be used, but can't be moved, otherwise machines just hang > after hotplug events. That was the only special ugly case we've > spotted during testing. I'll check if it will be enough just to work > around the 0xa. "nomodeset" is not really documented and is a funny way to say "don't bind video drivers that know about it", but OK. Thanks for checking on the other BARs. > > > +bool pci_movable_bars_enabled(void); > > > > I would really like it if this were simply > > > >extern bool pci_no_movable_bars; > > > > in drivers/pci/pci.h. It would default to false since it's > > uninitialized, and "pci=no_movable_bars" would set it to true. > > I have a premonition of platforms that will not support the feature. > Wouldn't be better to put this variable-flag to include/linux/pci.h , > so code in arch/* can set it, so they could work by default, without > the command line argument? In general I don't see why a platform wouldn't support this since there really isn't anything platform-specific here. But if a platform does need to disable it, having arch code set this flag sounds reasonable. We shouldn't make it globally visible until we actually need that, though. > > We have similar "=off" and "=force" parameters for ASPM and other > > things, and it makes the code really hard to analyze. The "=off" and "=force" things are the biggest things I'd like to avoid. Bjorn
Re: [PATCH v5 03/23] PCI: hotplug: Add a flag for the movable BARs feature
Hello David, On 9/30/19 11:44 AM, David Laight wrote: From: Bjorn Helgaas Sent: 27 September 2019 23:02 On Fri, Aug 16, 2019 at 07:50:41PM +0300, Sergey Miroshnichenko wrote: When hot-adding a device, the bridge may have windows not big enough (or fragmented too much) for newly requested BARs to fit in. And expanding these bridge windows may be impossible because blocked by "neighboring" BARs and bridge windows. Still, it may be possible to allocate a memory region for new BARs with the following procedure: 1) notify all the drivers which support movable BARs to pause and release the BARs; the rest of the drivers are guaranteed that their devices will not get BARs moved; 2) release all the bridge windows except of root bridges; 3) try to recalculate new bridge windows that will fit all the BAR types: - fixed; - immovable; - movable; - newly requested by hot-added devices; 4) if the previous step fails, disable BARs for one of the hot-added devices and retry from step 3; 5) notify the drivers, so they remap BARs and resume. You don't do the actual recalculation in *this* patch, but since you mention the procedure here, are we confident that we never make things worse? It's possible that a hot-add will trigger this attempt to move things around, and it's possible that we won't find space for the new device even if we move things around. But are we certain that every device that worked *before* the hot-add will still work *afterwards*? Much of the assignment was probably done by the BIOS using different algorithms than Linux has, so I think there's some chance that the BIOS did a better job and if we lose that BIOS assignment, we might not be able to recreate it. Yep, removing everything and starting again is probably OTT and most of the churn won't help. I think you need to work out what can be moved in order to make the required resources available to each bus and then make the required changes. In the simplest case you are trying to add resource below a bridge so need to 'shuffle' everything allocated after that bridge to later addresses (etc). Thank you for the review and suggestions! But a bridge window may be fragmented: its total free space is enough to fit everything, but no sufficient gaps for the new BARs. And this bridge window may be jammed between two immovable/fixed BARs. Or there may be lots of empty spaces in lower addresses after un-plugs, but everything if fixed/immovable on higher addresses. I've spent some time thinking on an optimization technique which can be efficient enough (touch as few BARs as possible) with as high success rate as calculating from scratch - and concluded that it is not worth it: if only release the "obstructing" BARs and bridge windows, a hotplug event will affect a half of (n+m) on average, which is still O(n+m), where n is a number of endpoints, and m is a number of bridges. But it's still need to resize windows of a root and other common bridges. Calculating bridge windows from scratch is relatively straightforward and fast, so I have just added support for fixed/immovable BARs there and reused. Many devices that support address reassignment might not need to be moved - so there is no point remmapping them. And it's the same algorithm that allocated BARs in first place, so it will reassign the same BARs for the non-affected part of the topology. There is also the case when a device that is present but not currently is use could be taken through a remove+insert sequence in order to change its resources. Much easier to implement than 'remap while active'. This would require a call into the driver (than can sleep) to request whether it is idle. (and probably one at the end if the remove wasn't done). Unbind+rebind the "immovable" drivers of non-opened devices may increase the probability of successful BAR allocation, but I'm afraid this will produce some amount of false hotplug-like events in the logs. Probably also some undesired effects like spikes in power consumption because of driver initialization. Best regards, Serge David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
Re: [PATCH v5 03/23] PCI: hotplug: Add a flag for the movable BARs feature
Hello Bjorn,
On 9/28/19 1:02 AM, Bjorn Helgaas wrote:
On Fri, Aug 16, 2019 at 07:50:41PM +0300, Sergey Miroshnichenko wrote:
When hot-adding a device, the bridge may have windows not big enough (or
fragmented too much) for newly requested BARs to fit in. And expanding
these bridge windows may be impossible because blocked by "neighboring"
BARs and bridge windows.
Still, it may be possible to allocate a memory region for new BARs with the
following procedure:
1) notify all the drivers which support movable BARs to pause and release
the BARs; the rest of the drivers are guaranteed that their devices will
not get BARs moved;
2) release all the bridge windows except of root bridges;
3) try to recalculate new bridge windows that will fit all the BAR types:
- fixed;
- immovable;
- movable;
- newly requested by hot-added devices;
4) if the previous step fails, disable BARs for one of the hot-added
devices and retry from step 3;
5) notify the drivers, so they remap BARs and resume.
You don't do the actual recalculation in *this* patch, but since you
mention the procedure here, are we confident that we never make things
worse?
It's possible that a hot-add will trigger this attempt to move things
around, and it's possible that we won't find space for the new device
even if we move things around. But are we certain that every device
that worked *before* the hot-add will still work *afterwards*?
Much of the assignment was probably done by the BIOS using different
algorithms than Linux has, so I think there's some chance that the
BIOS did a better job and if we lose that BIOS assignment, we might
not be able to recreate it.
If a hardware has some special constraints on BAR assignment that the
kernel is not aware of yet, the movable BARs may break things after a
hotplug event. So the feature must be disabled there (manually) until
the kernel get support for that special needs.
On x86 we had no choice - most of the machines we used just can't boot
with even an "empty" 16-port switch connected. So we hot-add it after
the boot, then trigger a rescan via 'echo 1 > /sys/bus/pci/rescan'.
And reserved bridge windows wasn't enough, and they can't expand
because are blocked by the next device.
This makes the prior reservation of memory by BIOS/bootloader/firmware not
required anymore for the PCI hotplug.
Drivers indicate their support of movable BARs by implementing the new
.rescan_prepare() and .rescan_done() hooks in the struct pci_driver. All
device's activity must be paused during a rescan, and iounmap()+ioremap()
must be applied to every used BAR.
The platform also may need to prepare to BAR movement, so new hooks added:
pcibios_rescan_prepare(pci_dev) and pcibios_rescan_prepare(pci_dev).
This patch is a preparation for future patches with actual implementation,
and for now it just does the following:
- declares the feature;
- defines pci_movable_bars_enabled(), pci_dev_movable_bars_supported(dev);
- invokes the .rescan_prepare() and .rescan_done() driver notifiers;
- declares and invokes the pcibios_rescan_prepare()/_done() hooks;
- adds the PCI_IMMOVABLE_BARS flag.
The feature is disabled by default (via PCI_IMMOVABLE_BARS) until the final
patch of the series. It can be overridden per-arch using this flag or by
the following command line option:
pcie_movable_bars={ off | force }
CC: Sam Bobroff
CC: Rajat Jain
CC: Lukas Wunner
CC: Oliver O'Halloran
CC: David Laight
Signed-off-by: Sergey Miroshnichenko
---
.../admin-guide/kernel-parameters.txt | 7 ++
drivers/pci/pci-driver.c | 2 +
drivers/pci/pci.c | 24 ++
drivers/pci/pci.h | 2 +
drivers/pci/probe.c | 86 ++-
include/linux/pci.h | 7 ++
6 files changed, 126 insertions(+), 2 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt
b/Documentation/admin-guide/kernel-parameters.txt
index 47d981a86e2f..e2274ee87a35 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3526,6 +3526,13 @@
nomsi Do not use MSI for native PCIe PME signaling (this makes
all PCIe root ports use INTx for all services).
+ pcie_movable_bars=[PCIE]
This isn't a PCIe-specific feature, it's just a function of whether
drivers are smart enough, so we shouldn't tie it specifically to PCIe.
We could eventually do this for conventional PCI as well.
+ Override the movable BARs support detection:
+ off
+ Disable even if supported by the platform
+ force
+ Enable even if not explicitly declared as supported
What's the need for "force"? If it's possible, I think we should
enable this functionality all the time and just have a disable switch
in
RE: [PATCH v5 03/23] PCI: hotplug: Add a flag for the movable BARs feature
From: Bjorn Helgaas > Sent: 27 September 2019 23:02 > On Fri, Aug 16, 2019 at 07:50:41PM +0300, Sergey Miroshnichenko wrote: > > When hot-adding a device, the bridge may have windows not big enough (or > > fragmented too much) for newly requested BARs to fit in. And expanding > > these bridge windows may be impossible because blocked by "neighboring" > > BARs and bridge windows. > > > > Still, it may be possible to allocate a memory region for new BARs with the > > following procedure: > > > > 1) notify all the drivers which support movable BARs to pause and release > >the BARs; the rest of the drivers are guaranteed that their devices will > >not get BARs moved; > > > > 2) release all the bridge windows except of root bridges; > > > > 3) try to recalculate new bridge windows that will fit all the BAR types: > >- fixed; > >- immovable; > >- movable; > >- newly requested by hot-added devices; > > > > 4) if the previous step fails, disable BARs for one of the hot-added > >devices and retry from step 3; > > > > 5) notify the drivers, so they remap BARs and resume. > > You don't do the actual recalculation in *this* patch, but since you > mention the procedure here, are we confident that we never make things > worse? > > It's possible that a hot-add will trigger this attempt to move things > around, and it's possible that we won't find space for the new device > even if we move things around. But are we certain that every device > that worked *before* the hot-add will still work *afterwards*? > > Much of the assignment was probably done by the BIOS using different > algorithms than Linux has, so I think there's some chance that the > BIOS did a better job and if we lose that BIOS assignment, we might > not be able to recreate it. Yep, removing everything and starting again is probably OTT and most of the churn won't help. I think you need to work out what can be moved in order to make the required resources available to each bus and then make the required changes. In the simplest case you are trying to add resource below a bridge so need to 'shuffle' everything allocated after that bridge to later addresses (etc). Many devices that support address reassignment might not need to be moved - so there is no point remmapping them. There is also the case when a device that is present but not currently is use could be taken through a remove+insert sequence in order to change its resources. Much easier to implement than 'remap while active'. This would require a call into the driver (than can sleep) to request whether it is idle. (and probably one at the end if the remove wasn't done). David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
Re: [PATCH v5 03/23] PCI: hotplug: Add a flag for the movable BARs feature
On Fri, Aug 16, 2019 at 07:50:41PM +0300, Sergey Miroshnichenko wrote:
> When hot-adding a device, the bridge may have windows not big enough (or
> fragmented too much) for newly requested BARs to fit in. And expanding
> these bridge windows may be impossible because blocked by "neighboring"
> BARs and bridge windows.
>
> Still, it may be possible to allocate a memory region for new BARs with the
> following procedure:
>
> 1) notify all the drivers which support movable BARs to pause and release
>the BARs; the rest of the drivers are guaranteed that their devices will
>not get BARs moved;
>
> 2) release all the bridge windows except of root bridges;
>
> 3) try to recalculate new bridge windows that will fit all the BAR types:
>- fixed;
>- immovable;
>- movable;
>- newly requested by hot-added devices;
>
> 4) if the previous step fails, disable BARs for one of the hot-added
>devices and retry from step 3;
>
> 5) notify the drivers, so they remap BARs and resume.
You don't do the actual recalculation in *this* patch, but since you
mention the procedure here, are we confident that we never make things
worse?
It's possible that a hot-add will trigger this attempt to move things
around, and it's possible that we won't find space for the new device
even if we move things around. But are we certain that every device
that worked *before* the hot-add will still work *afterwards*?
Much of the assignment was probably done by the BIOS using different
algorithms than Linux has, so I think there's some chance that the
BIOS did a better job and if we lose that BIOS assignment, we might
not be able to recreate it.
> This makes the prior reservation of memory by BIOS/bootloader/firmware not
> required anymore for the PCI hotplug.
>
> Drivers indicate their support of movable BARs by implementing the new
> .rescan_prepare() and .rescan_done() hooks in the struct pci_driver. All
> device's activity must be paused during a rescan, and iounmap()+ioremap()
> must be applied to every used BAR.
>
> The platform also may need to prepare to BAR movement, so new hooks added:
> pcibios_rescan_prepare(pci_dev) and pcibios_rescan_prepare(pci_dev).
>
> This patch is a preparation for future patches with actual implementation,
> and for now it just does the following:
> - declares the feature;
> - defines pci_movable_bars_enabled(), pci_dev_movable_bars_supported(dev);
> - invokes the .rescan_prepare() and .rescan_done() driver notifiers;
> - declares and invokes the pcibios_rescan_prepare()/_done() hooks;
> - adds the PCI_IMMOVABLE_BARS flag.
>
> The feature is disabled by default (via PCI_IMMOVABLE_BARS) until the final
> patch of the series. It can be overridden per-arch using this flag or by
> the following command line option:
>
> pcie_movable_bars={ off | force }
>
> CC: Sam Bobroff
> CC: Rajat Jain
> CC: Lukas Wunner
> CC: Oliver O'Halloran
> CC: David Laight
> Signed-off-by: Sergey Miroshnichenko
> ---
> .../admin-guide/kernel-parameters.txt | 7 ++
> drivers/pci/pci-driver.c | 2 +
> drivers/pci/pci.c | 24 ++
> drivers/pci/pci.h | 2 +
> drivers/pci/probe.c | 86 ++-
> include/linux/pci.h | 7 ++
> 6 files changed, 126 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> index 47d981a86e2f..e2274ee87a35 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3526,6 +3526,13 @@
> nomsi Do not use MSI for native PCIe PME signaling (this makes
> all PCIe root ports use INTx for all services).
>
> + pcie_movable_bars=[PCIE]
This isn't a PCIe-specific feature, it's just a function of whether
drivers are smart enough, so we shouldn't tie it specifically to PCIe.
We could eventually do this for conventional PCI as well.
> + Override the movable BARs support detection:
> + off
> + Disable even if supported by the platform
> + force
> + Enable even if not explicitly declared as supported
What's the need for "force"? If it's possible, I think we should
enable this functionality all the time and just have a disable switch
in case we trip over cases where it doesn't work, e.g., something
like:
pci=no_movable_bars
> pcmv= [HW,PCMCIA] BadgePAD 4
>
> pd_ignore_unused
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index a8124e47bf6e..d11909e79263 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -1688,6 +1688,8 @@ static int __init pci_driver_init(void)
> {
> int ret;
>
> + pci_add_flags(PCI_IMMOVABLE_BARS);
> +
> ret =
