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From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Wed, 12 Jun 2024 21:07:09 +0200
Message-ID: <CAJZ5v0hFYSQic3N2KWGzyrX-K4KX9Okt20NtXmqRuutc140HUw@mail.gmail.com>
Subject: Re: [PATCH 1/1] ACPI: scan: Ignore Dell XPS 9320 camera graph port nodes
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Hans de Goede <hdegoede@redhat.com>, "Rafael J. Wysocki" <rafael@kernel.org>, 
	Sakari Ailus <sakari.ailus@linux.intel.com>, Genes Lists <lists@sapience.com>, 
	linux-kernel@vger.kernel.org, mchehab@kernel.org, hverkuil-cisco@xs4all.nl, 
	wentong.wu@intel.com, linux-media@vger.kernel.org, linux-acpi@vger.kernel.org, 
	"regressions@lists.linux.dev" <regressions@lists.linux.dev>
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Hi Laurent,

On Wed, Jun 12, 2024 at 4:40=E2=80=AFPM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> On Wed, Jun 12, 2024 at 04:30:30PM +0200, Hans de Goede wrote:
> > On 6/12/24 3:06 PM, Rafael J. Wysocki wrote:
> > > On Wed, Jun 12, 2024 at 2:47=E2=80=AFPM Sakari Ailus wrote:
> > >> On Wed, Jun 12, 2024 at 02:32:26PM +0200, Rafael J. Wysocki wrote:
> > >>>>>>> I just hit the same problem on another Dell laptop. It seems th=
at
> > >>>>>>> all Dell laptops with IPU6 camera from the Tiger Lake, Alder La=
ke
> > >>>>>>> and Raptor Lake generations suffer from this problem.
> > >>>>>>>
> > >>>>>>> So instead of playing whack a mole with DMI matches we should
> > >>>>>>> simply disable ACPI MIPI DISCO support on all Dell laptops
> > >>>>>>> with those CPUs. I'm preparing a fix for this to replace
> > >>>>>>> the DMI matching now.
> > >>>>>>
> > >>>>>> DisCo for Imaging support shouldn't be dropped on these systems,=
 and this
> > >>>>>> isn't what your patch does either. Instead the ACPI graph port n=
odes (as
> > >>>>>> per Linux specific definitions) are simply dropped, i.e. this is=
n't related
> > >>>>>> to DisCo for Imaging at all.
> > >>>>>
> > >>>>> So it looks like the changelog of that patch could be improved, r=
ight?
> > >>>>
> > >>>> Well, yes. The reason the function is in the file is that nearly a=
ll camera
> > >>>> related parsing is located there, not that it would be related to =
DisCo for
> > >>>> Imaging as such.
> > >>>
> > >>> So IIUC the camera graph port nodes are created by default with the
> > >>> help of the firmware-supplied information, but if that is defective=
 a
> > >>> quirk can be added to skip the creation of those ports in which cas=
e
> > >>> they will be created elsewhere.
> > >>>
> > >>> Is this correct?
> > >>
> > >> Yes.
> > >
> > > So it would be good to add a comment to this effect to
> > > acpi_nondev_subnode_extract() where acpi_graph_ignore_port() is
> > > called.
> > >
> > > And there is a somewhat tangential question that occurred to me: If
> > > the nodes are created elsewhere when acpi_graph_ignore_port() is true=
,
> > > why is it necessary to consult the platform firmware for the
> > > information on them at all?  Wouldn't it be better to simply always
> > > create them elsewhere?
> >
> > That is a good question. The ACPI MIPI DISCO specification is an
> > attempt standardize how MIPI cameras and their sensors are described
> > in ACPI.
> >
> > But this is not actually being used by any Windows drivers atm. The win=
dows
> > drivers rely on their own custom ACPI data which gets translated into
> > standard Linux device-properties by: drivers/media/pci/intel/ipu-bridge=
.c
> >
> > and so far AFAIK there are 0 laptops where there actually is 100% funct=
ional
> > ACPI MIPI information. I believe that some work is in place to get corr=
ect
> > usable ACPI MIPI information in place in the ACPI tables of some Meteor=
 Lake
> > laptops. But I believe that there too it does not work yet with the BIO=
S
> > version with which current Windows models are shipping. It is being fix=
ed
> > for systems which have Linux support from the vendor but I suspect that
>
> I think it's shipped in Chrome Books. Sakari can confirm.
>
> > on other models if ACPI MIPI DISCO information is there it will not
> > necessarily be reliable because AFAICT Windows does not actually use it=
.
> >
> > And TBH this has me worried about camera support for Meteor Lake device=
s
> > going forward. We really need to have 1 reliable source of truth here a=
nd
> > using information which is ignored by Windows does not seem like the be=
st
> > source to use.
>
> As long as the Windows drivers don't use the ACPI data that Linux uses,
> you can be 100% sure it will be wrong. That will never be fixed if Intel
> doesn't address the issue on their side, and effort we would put in
> standardizing that data for machines shipped by Windows OEMs is a waste
> of time in my opinion. Our only option, given Intel's failure, is to
> keep reverse-engineering camera support per machine for the time being
> (sometimes with the help of OEMs).

So while I kind of agree with you on the technical side (as you can
see from my messages in this thread), there is one thing in the above
paragraph that I need to react to.

Namely, both I and Sakari are Intel employees.  Do you think or are
you suggesting that we are somehow responsible for this failure?
Because I personally don't think like I have anything to do with it.

What do you mean, specifically, by saying "if Intel doesn't address
the issue on their side"?  And who at Intel do I need to talk to about
this?