On Tue, 12 Jan 2021 at 23:49, Bjorn Helgaas <helg...@kernel.org> wrote: > > On Sat, Jan 09, 2021 at 10:53:53AM +0100, Ard Biesheuvel wrote: > > The _DSM #5 method in the ACPI host bridge object tells us whether the > > OS is permitted to deviate from the resource assignment configured by > > the firmware. If this is not the case, we should not permit drivers to > > resize BARs on the fly. So make pci_resize_resource() take this into > > account. > > > > Cc: <sta...@vger.kernel.org> # v5.4+ > > Signed-off-by: Ard Biesheuvel <a...@kernel.org> > > Capitalized subject to match convention and applied to pci/resource > for v5.11, thanks! > > Is there an email, bug report, etc that prompted this change? >
No, I was just reviewing the recent Tianocore changes to perform BAR resizing before resource assignment even takes places, which is obviously a more appropriate time to do it, as it does not require the OS to modify the firmware configuration at all. This reminded me of _DSM #5 and the fact that the OS may not even be permitted to make any changes. > > --- > > drivers/pci/setup-res.c | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c > > index 43eda101fcf4..3b38be081e93 100644 > > --- a/drivers/pci/setup-res.c > > +++ b/drivers/pci/setup-res.c > > @@ -410,10 +410,16 @@ EXPORT_SYMBOL(pci_release_resource); > > int pci_resize_resource(struct pci_dev *dev, int resno, int size) > > { > > struct resource *res = dev->resource + resno; > > + struct pci_host_bridge *host; > > int old, ret; > > u32 sizes; > > u16 cmd; > > > > + /* Check if we must preserve the firmware's resource assignment */ > > + host = pci_find_host_bridge(dev->bus); > > + if (host->preserve_config) > > + return -ENOTSUPP; > > + > > /* Make sure the resource isn't assigned before resizing it. */ > > if (!(res->flags & IORESOURCE_UNSET)) > > return -EBUSY; > > -- > > 2.17.1 > >