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

From: Jani Nikula <jani.nikula@linux.intel.com>
To: Rajat Jain <rajatja@google.com>
Cc: "Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
	"Maxime Ripard" <mripard@kernel.org>,
	"Sean Paul" <sean@poorly.run>, "David Airlie" <airlied@linux.ie>,
	"Daniel Vetter" <daniel@ffwll.ch>,
	"Joonas Lahtinen" <joonas.lahtinen@linux.intel.com>,
	"Rodrigo Vivi" <rodrigo.vivi@intel.com>,
	"Ville Syrjälä" <ville.syrjala@linux.intel.com>,
	"Chris Wilson" <chris@chris-wilson.co.uk>,
	"Imre Deak" <imre.deak@intel.com>,
	"José Roberto de Souza" <jose.souza@intel.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	intel-gfx@lists.freedesktop.org,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Mat King" <mathewk@google.com>,
	"Daniel Thompson" <daniel.thompson@linaro.org>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Pavel Machek" <pavel@denx.de>, "Sean Paul" <seanpaul@google.com>,
	"Duncan Laurie" <dlaurie@google.com>,
	"Jesse Barnes" <jsbarnes@google.com>,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"Mark Pearson" <mpearson@lenovo.com>,
	"Nitin Joshi1" <njoshi1@lenovo.com>,
	"Sugumaran Lacshiminarayanan" <slacshiminar@lenovo.com>,
	"Tomoki Maruichi" <maruichit@lenovo.com>,
	"Rajat Jain" <rajatxjain@gmail.com>
Subject: Re: [PATCH v6 2/3] drm/i915: Lookup and attach ACPI device node for connectors
Date: Fri, 06 Mar 2020 11:42:00 +0200	[thread overview]
Message-ID: <87tv31om53.fsf@intel.com> (raw)
In-Reply-To: <CACK8Z6HRB9q1KeborGr7V-0Qp0AApHV6gBTkc6xD5NokH8gr0w@mail.gmail.com>

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.

>> 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