Hi,
On Fri, 2019-05-10 at 16:54 +0200, Daniel Vetter wrote:
> On Fri, May 10, 2019 at 2:12 PM Paul Kocialkowski
> <paul.kocialkow...@bootlin.com> wrote:
> > Hi,
> >
> > On Tue, 2019-05-07 at 21:57 +0530, Ramalingam C wrote:
> > > DRM API for generating uevent for a status changes of connector's
> > > property.
> > >
> > > This uevent will have following details related to the status change:
> > >
> > > HOTPLUG=1, CONNECTOR=<connector_id> and PROPERTY=<property_id>
> > >
> > > Need ACK from this uevent from userspace consumer.
> >
> > So we just had some discussions over on IRC and at about the hotplug
> > issue and came up with similar ideas:
> > https://lists.freedesktop.org/archives/dri-devel/2019-May/217408.html
> >
> > The conclusions of these discussions so far would be to have a more or
> > less fine grain of uevent reporting depending on what happened. The
> > point is that we need to cover different cases:
> > - one or more properties changed;
> > - the connector status changed;
> > - something else about the connector changed (e.g. EDID/modes)
> >
> > For the first case, we can send out:
> > HOTPLUG=1
> > CONNECTOR=<id>
> > PROPERTY=<id>
> >
> > and no reprobe is required.
> >
> > For the second one, something like:
> > HOTPLUG=1
> > CONNECTOR=<id>
> > STATUS=Connected/Disconnected
> >
> > and a connector probe is needed for connected, but not for
> > disconnected;
> >
> > For the third one, we can only indicate the connector:
> > HOTPLUG=1
> > CONNECTOR=<id>
> >
> > and a reprobe of the connector is always needed
>
> There's no material difference between this one and the previous one.
> Plus there's no beenfit in supplying the actual value of the property,
> i.e. we can reuse the same PROPERTY=<id-of-status-property> trick.
That's the idea, but we need to handle status changes differently than
properties, since as far as I know, connected/unconnected status is not
exposed as a prop for the connector.
> Here's why:
> - A side effect of forcing a probe on a connector is that you get to
> read all the properties, so supplying them is kinda pointless.
Agreed, except for the status case where it's useful to know it's a
disconnect, because we don't need any probe step in that case.
> - You can read STATUS without forcing a reprobe, if you want to avoid
> the reprobe for disconnected. I'd kinda not recommend that though,
> feels a bit like overoptimizing. And for reasonable connectors (i.e.
> dp) reprobing a disconnected output is fast. HDMI is ... less
> reasonable unfortunately, but oh well.
How would that be retreived then? From the looks of it, that's a
MODE_GETCONNECTOR ioctl and I was under the impression this is what
does the full reprobe.
Not sure what issues could arise in case of disconnect without reprobe
-- at least I don't see why userspace should have to do anything in
particular except no longer using the connector, even in complex DP MST
cases.
> - There's no way to only reprobe status, you can only ever reprobe
> everything with the current ioctl and implementations. Having an
> option to reprobe only parts of it doesn't seem useful to me (we need
> to read the EDID anyway, and that's the expensive part of reprobing in
> almost all cases).
Agreed.
> In a way PROPERTY=<status-prop-id> simply tells userspace that it
> needs to reprobe this connector.
I thought we could access the props alone, which avoids doing a reprobe
when the kernel knows that only a prop or a set of props changed and do
not require a full reprobe. That's the first case I was mentionning.
> At that point we need to figure out whether this is a good uapi or
> not, and that's where the epoch comes in. There's two reasons for an
> epoch:
> - We need it internally because I'm not goinig to wire a new return
> value through hundreds of connector probe functions. It's much easier
> to have an epoch counter which we set from e.g. drm_set_edid and
> similar functions that update probe state.
I don't think I'm following what issue this is trying to solve
internally.
> - If userspace misses an event and there's no epoch, we're forcing
> userspace to reprobe everything. Use case would be if a compositor is
> switched away we probably don't want to piss of the current compositor
> by blocking it's own probe kernel calls by doing our own (probe is
> single-threaded in the kernel through the dev->mode_config.mutex). If
> it can read the epoch property (which it can do without forcing a
> reprobe) userspace would know which connectors it needs to check and
> reprobe.
>
> Hence why epoch, it's a bit more robust userspace api. Ofc you could
> also require that userspace needs to keep parsing all uevents and make
> a list of all connectors it needs to reprobe when it's back to being
> the active compositor. But just comparing a current epoch with the one
> you cached from the last full probe is much easier.
Fair enough, I think it's a fine idea for robustness yes, but I think
we could also provide extra info in the uevent when relevant and not
rely on that entirely.
> Another thing: None of this we can for connectors with unreliable hdp.
> Or at least you'll piss of users if you cache always. The sad thing is
> that HDMI is unreliable, at least on some machines/screen combos (you
> never get a hpd irq if you plug in/unplug). So real compositors still
> need to reprobe when the user asks for it. igt can probably get away
> without reprobing.
I wonder how that is handled currently and how a user action can solve
the issue without any notification from the kernel. Maybe a need a
better understanding of that case to have a clearer idea.
Cheers,
Paul
> -Daniel
>
> > Then we still have the legacy case:
> > HOTPLUG=1
> >
> > where userspace is expected to reprobe all the connectors.
> >
> > I think this would deserve to be a separate series on its own. So I am
> > proposing to take this one off your plate and come up with another
> > seres implementing this proposal. What do you think?
> >
> > Cheers,
> >
> > Paul
> >
> > > v2:
> > > Minor fixes at KDoc comments [Daniel]
> > > v3:
> > > Check the property is really attached with connector [Daniel]
> > >
> > > Signed-off-by: Ramalingam C <ramalinga...@intel.com>
> > > Reviewed-by: Daniel Vetter <daniel.vet...@ffwll.ch>
> > > ---
> > > drivers/gpu/drm/drm_sysfs.c | 35 +++++++++++++++++++++++++++++++++++
> > > include/drm/drm_sysfs.h | 5 ++++-
> > > 2 files changed, 39 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c
> > > index 18b1ac442997..63fa951a20db 100644
> > > --- a/drivers/gpu/drm/drm_sysfs.c
> > > +++ b/drivers/gpu/drm/drm_sysfs.c
> > > @@ -21,6 +21,7 @@
> > > #include <drm/drm_sysfs.h>
> > > #include <drm/drmP.h>
> > > #include "drm_internal.h"
> > > +#include "drm_crtc_internal.h"
> > >
> > > #define to_drm_minor(d) dev_get_drvdata(d)
> > > #define to_drm_connector(d) dev_get_drvdata(d)
> > > @@ -320,6 +321,9 @@ void drm_sysfs_lease_event(struct drm_device *dev)
> > > * Send a uevent for the DRM device specified by @dev. Currently we only
> > > * set HOTPLUG=1 in the uevent environment, but this could be expanded to
> > > * deal with other types of events.
> > > + *
> > > + * Any new uapi should be using the drm_sysfs_connector_status_event()
> > > + * for uevents on connector status change.
> > > */
> > > void drm_sysfs_hotplug_event(struct drm_device *dev)
> > > {
> > > @@ -332,6 +336,37 @@ void drm_sysfs_hotplug_event(struct drm_device *dev)
> > > }
> > > EXPORT_SYMBOL(drm_sysfs_hotplug_event);
> > >
> > > +/**
> > > + * drm_sysfs_connector_status_event - generate a DRM uevent for connector
> > > + * property status change
> > > + * @connector: connector on which property status changed
> > > + * @property: connector property whoes status changed.
> > > + *
> > > + * Send a uevent for the DRM device specified by @dev. Currently we
> > > + * set HOTPLUG=1 and connector id along with the attached property id
> > > + * related to the status change.
> > > + */
> > > +void drm_sysfs_connector_status_event(struct drm_connector *connector,
> > > + struct drm_property *property)
> > > +{
> > > + struct drm_device *dev = connector->dev;
> > > + char hotplug_str[] = "HOTPLUG=1", conn_id[30], prop_id[30];
> > > + char *envp[4] = { hotplug_str, conn_id, prop_id, NULL };
> > > +
> > > + WARN_ON(!drm_mode_obj_find_prop_id(&connector->base,
> > > + property->base.id));
> > > +
> > > + snprintf(conn_id, ARRAY_SIZE(conn_id),
> > > + "CONNECTOR=%u", connector->base.id);
> > > + snprintf(prop_id, ARRAY_SIZE(prop_id),
> > > + "PROPERTY=%u", property->base.id);
> > > +
> > > + DRM_DEBUG("generating connector status event\n");
> > > +
> > > + kobject_uevent_env(&dev->primary->kdev->kobj, KOBJ_CHANGE, envp);
> > > +}
> > > +EXPORT_SYMBOL(drm_sysfs_connector_status_event);
> > > +
> > > static void drm_sysfs_release(struct device *dev)
> > > {
> > > kfree(dev);
> > > diff --git a/include/drm/drm_sysfs.h b/include/drm/drm_sysfs.h
> > > index 4f311e836cdc..d454ef617b2c 100644
> > > --- a/include/drm/drm_sysfs.h
> > > +++ b/include/drm/drm_sysfs.h
> > > @@ -4,10 +4,13 @@
> > >
> > > struct drm_device;
> > > struct device;
> > > +struct drm_connector;
> > > +struct drm_property;
> > >
> > > int drm_class_device_register(struct device *dev);
> > > void drm_class_device_unregister(struct device *dev);
> > >
> > > void drm_sysfs_hotplug_event(struct drm_device *dev);
> > > -
> > > +void drm_sysfs_connector_status_event(struct drm_connector *connector,
> > > + struct drm_property *property);
> > > #endif
> > --
> > Paul Kocialkowski, Bootlin
> > Embedded Linux and kernel engineering
> > https://bootlin.com
> >
>
>
--
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com
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