Re: [PATCH v3 0/3] Send a hotplug when edid changes

["Lisovskiy, Stanislav" <stanislav.lisovskiy@intel.com>]

On Tue, 2019-09-03 at 11:40 +0200, Daniel Vetter wrote:
> 
> > > In fact I was wrong - when it worked, it was using exactly those
> > > patches :). With clean drm-tip - it seems to work ocassionally
> > > and it
> > > doesn't update the actual display edid and other stuff, so even
> > > when
> > > displays are changed we still see the old info/edid from
> > > userspace.
> > > 
> > > We always get a hpd irq when suspend/resume however it doesn't
> > > always
> > > result in uevent being sent. So there is a real need in those
> > > patches.
> > > 
> > 
> > Just decided to "ping" this discussion again. The issue is already
> > some
> > years old and still nothing is fixed. I do agree that may be
> > something
> > needs to be fixed/changed here in those patches, but something must
> > be
> > agreed at least I guess, as discussions themself do not fix bugs.
> > Currently those patches address a particular issue which occurs, if
> > display is changed during suspend. 
> > On ocassional basis, userspace might not get a hotplug event at
> > all,
> > causing different kind of problems(like wrong mode set on display
> > or
> > diaply not working at all). Also some kms_chamelium hotplug tests
> > fail
> > because of that. 
> 
> I still think we'll long-term regret this if we just duct-tape more
> stuff
> on top, instead of giving userspace a more informative uevent. This
> will
> send more uevents to userspace, so maybe then userspace tries to
> filter
> more and be clever, which never works, and we're back to tears.

But here we actually do need a uevent as currently we don't get any at
all, if edid changes during suspend. If userspace will try to filter
this out - it's just stupid, however we still need to do things
correctly.

> 
> Anyway, on the approach itself: It's extremely i915 specific, and it
> requires that all drivers roll out drm_edid_equal checks and not
> forget to
> increment the epoch counter.

> 
> What I had in mind is that when we set the edid for a connector with
> drm_connector_update_edid_property() or whatever, then the epoch
> counter
> would auto-increment if anything has changed. Similarly (long-term
> idea at
> least) if anything important with DP registers has changed.
> 
> Can't we do that, instead of this sub-optimal solution of requiring
> all
> drivers to roll out lots of code?

1) We update edid in intel_dp_set_edid, which is called from
intel_dp_detect(drm_connector_helper_funcs->detect_ctx hook) which is
called from drm_helper_probe_detect. That one is called either from
specific intel_encoder->hotplug hook in i915_hotplug_work_func or by
userspace request during reprobe.

2) Previously we were simply updating edid in intel_dp_set_edid without
caring if it is the same or not and hotplug event was sent only once
connection_status had changed. 

3) drm_connector_update_edid_property is called from connector-
>get_modes hook(lets say intel_dp_get_modes fo dp) however it simply
uses results of
drm_helper_probe_detect so without actual comparison it would not be
able to detect if we really need to update epoch_counter or not.

Because as I said currently intel_dp_set_edid simply assigns it without
checking, so that way you will get epoch_counter updated every time,
i.e exactly what you wanted to avoid here.

So we really need someway to determine if edid had changed, instead of
simply assigning it all the time - that is why I had to make this
function.

Cheers,

Stanislav


> -Daniel
> 
> > 
> > > > 
> > > > > 
> > > > > - Stanislav
> > > > > 
> > > > > > 
> > > > > > 
> > > > > > > 
> > > > > > > -Stanislav
> > > > > > > 
> > > > > > > > 
> > > > > > > > Cheers, Daniel
> > > > > > > > 
> > > > > > > > > 
> > > > > > > > > 
> > > > > > > > > -Stanislav
> > > > > > > > > 
> > > > > > > > > 
> > > > > > > > > > -Daniel
> > > > > > > > > > 
> > > > > > > > > > > 
> > > > > > > > > > > Stanislav Lisovskiy (3):
> > > > > > > > > > >   drm: Add helper to compare edids.
> > > > > > > > > > >   drm: Introduce change counter to drm_connector
> > > > > > > > > > >   drm/i915: Send hotplug event if edid had
> > > > > > > > > > > changed.
> > > > > > > > > > > 
> > > > > > > > > > >  drivers/gpu/drm/drm_connector.c              |  
> > > > > > > > > > > 1 +
> > > > > > > > > > >  drivers/gpu/drm/drm_edid.c                   |
> > > > > > > > > > > 33
> > > > > > > > > > > ++++++++++++++++++++
> > > > > > > > > > >  drivers/gpu/drm/drm_probe_helper.c           |
> > > > > > > > > > > 29
> > > > > > > > > > > +++++++++++++++-
> > > > > > > > > > > -
> > > > > > > > > > >  drivers/gpu/drm/i915/display/intel_dp.c      |
> > > > > > > > > > > 16
> > > > > > > > > > > +++++++++-
> > > > > > > > > > >  drivers/gpu/drm/i915/display/intel_hdmi.c    |
> > > > > > > > > > > 16
> > > > > > > > > > > ++++++++--
> > > > > > > > > > >  drivers/gpu/drm/i915/display/intel_hotplug.c |
> > > > > > > > > > > 21
> > > > > > > > > > > ++++++++++
> > > > > > > > > > > ---
> > > > > > > > > > >  include/drm/drm_connector.h                  |  
> > > > > > > > > > > 3 ++
> > > > > > > > > > >  include/drm/drm_edid.h                       |  
> > > > > > > > > > > 9
> > > > > > > > > > > ++++++
> > > > > > > > > > >  8 files changed, 117 insertions(+), 11
> > > > > > > > > > > deletions(-)
> > > > > > > > > > > 
> > > > > > > > > > > --
> > > > > > > > > > > 2.17.1
> > > > > > > > > > > 
> > > > > > > > > > 
> > > > > > > > > > 
> > > > > > > > 
> > > > > > > > 
> > > > > > > > 
> > > > > > 
> > > > > > 
> > > > 
> > > > 
> > > 
> > > _______________________________________________
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> > > dri-devel@lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> 
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