linux-kernel - Re: [PATCH v6 2/3] drm/i915: Lookup and attach ACPI device node for connectors

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Date:   Fri, 06 Mar 2020 11:42:00 +0200
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Rajat Jain <rajatja@...gle.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Imre Deak <imre.deak@...el.com>,
        José Roberto de Souza 
        <jose.souza@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        intel-gfx@...ts.freedesktop.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mat King <mathewk@...gle.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jonathan Corbet <corbet@....net>, Pavel Machek <pavel@...x.de>,
        Sean Paul <seanpaul@...gle.com>,
        Duncan Laurie <dlaurie@...gle.com>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Mark Pearson <mpearson@...ovo.com>,
        Nitin Joshi1 <njoshi1@...ovo.com>,
        Sugumaran Lacshiminarayanan <slacshiminar@...ovo.com>,
        Tomoki Maruichi <maruichit@...ovo.com>,
        Rajat Jain <rajatxjain@...il.com>
Subject: Re: [PATCH v6 2/3] drm/i915: Lookup and attach ACPI device node for connectors

On Thu, 05 Mar 2020, Rajat Jain <rajatja@...gle.com> wrote:
> On Thu, Mar 5, 2020 at 1:41 AM Jani Nikula <jani.nikula@...ux.intel.com> wrote:
>>
>> On Wed, 04 Mar 2020, Rajat Jain <rajatja@...gle.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.

>> 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.

>> (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