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From:   Rajat Jain <rajatja@google.com>
Date:   Mon, 9 Mar 2020 17:09:23 -0700
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Subject: Re: [PATCH v6 2/3] drm/i915: Lookup and attach ACPI device node for connectors
To:     Jani Nikula <jani.nikula@linux.intel.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
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On Fri, Mar 6, 2020 at 5:38 PM Rajat Jain <rajatja@google.com> wrote:
>
> On Fri, Mar 6, 2020 at 1:42 AM Jani Nikula <jani.nikula@linux.intel.com> wrote:
> >
> > On Thu, 05 Mar 2020, Rajat Jain <rajatja@google.com> wrote:
> > > On Thu, Mar 5, 2020 at 1:41 AM Jani Nikula <jani.nikula@linux.intel.com> wrote:
> > >>
> > >> On Wed, 04 Mar 2020, Rajat Jain <rajatja@google.com> wrote:
> > >> 1) See if we can postpone creating and attaching properties to connector
> > >> ->late_register hook. (I didn't have the time to look into it yet, at
> > >> all.)
> > >
> > > Apparently not. The drm core doesn't like to add properties in
> > > late_register() callback. I just tried it and get this warning:
> >
> > I kind of had a feeling this would be the case, thanks for checking.
>
> Thinking about it again, it looks like there is a difference in
> creating a property and attaching a property. I'm wondering if drm
> would let me (unconditionally) create a property before registering,
> and attach it in late_register() only in case a privacy screen is
> detected. (If not present, I can destroy the property in
> late_register()). If this approach sound more promising, I can try it
> out.

I tried out this approach, and it worked. The new patchset is posted at:

https://patchwork.freedesktop.org/series/74473/#rev1

Thanks!

Rajat

>
> >
> > >> 2) Provide a way to populate connector->acpi_device_id and
> > >> connector->acpi_handle on a per-connector basis. At least the device id
> > >> remains constant for the lifetime of the drm_device
> > >
> > > Are you confirming that the connector->acpi_device_id remains constant
> > > for the lifetime of the drm_device, as calculated in
> > > intel_acpi_device_id_update()?  Even in the face of external displays
> > > (monitors) being connected and disconnected during the lifetime of the
> > > system? If so, then I think we can have a solution.
> >
> > First I thought so. Alas it does not hold for DP MST, where you can have
> > connectors added and removed dynamically. I think we could ensure they
> > stay the same for all other connectors though. I'm pretty sure this is
> > already the case; they get added/removed after all others.
> >
> > Another thought, from the ACPI perspective, I'm not sure the dynamically
> > added/removed DP MST connectors should even have acpi handles. But
> > again, tying all this together with ACPI stuff is not something I am an
> > expert on.
>
> I propose that we:
>
> 1) Maintain a display_index[] array within the drm_dev, and increment
> as connectors are added.
> 2) Initialize connector->acpi_device_id and and connector->acpi_handle
> while registering (one time per connector).
> 3) Remove the code to update acpi_device_id on every resume.
>
> It doesn't look like anyone on the DP MST side has cared for ACPI so
> far, so I doubt if we can do anything that might break MST currently.
> In other words, the above should not make things any worse for MST, if
> not better. For connectors other than MST, this should allow them to
> get ACPI handle and play with it, if they need.
>
> WDYT?
>
> Thanks,
>
> Rajat
>
> >
> > >> (why do we keep
> > >> updating it at every resume?!) but can we be sure ->acpi_handle does
> > >> too? (I don't really know my way around ACPI.)
> > >
> > > I don't understand why this was being updated on every resume in that
> > > case (this existed even before my patchset). I believe we do not need
> > > it. Yes, the ->acpi_handle will not change if the ->acpi_device_id
> > > does not change. I believe the way forward should then be to populate
> > > connector->acpi_device_id and connector->acpi_handle ONE TIME at the
> > > time of connector init (and not update it on every resume). Does this
> > > sound ok?
> >
> > If a DP MST connector gets removed, should the other ACPI display
> > indexes after that shift, or remain the same? I really don't know.
> >
> > BR,
> > Jani.
> >
> > --
> > Jani Nikula, Intel Open Source Graphics Center