linux-kernel - Re: [PATCH 1/1] ACPI: scan: Ignore Dell XPS 9320 camera graph port nodes

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Date: Wed, 12 Jun 2024 15:06:53 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Hans de Goede <hdegoede@...hat.com>, 
	Genes Lists <lists@...ience.com>, linux-kernel@...r.kernel.org, mchehab@...nel.org, 
	hverkuil-cisco@...all.nl, laurent.pinchart@...asonboard.com, 
	wentong.wu@...el.com, linux-media@...r.kernel.org, linux-acpi@...r.kernel.org, 
	"regressions@...ts.linux.dev" <regressions@...ts.linux.dev>
Subject: Re: [PATCH 1/1] ACPI: scan: Ignore Dell XPS 9320 camera graph port nodes

Hi Sakari,

On Wed, Jun 12, 2024 at 2:47 PM Sakari Ailus
<sakari.ailus@...ux.intel.com> wrote:
>
> Hi Rafael,
>
> 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 that
> > > > > > all Dell laptops with IPU6 camera from the Tiger Lake, Alder Lake
> > > > > > 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 nodes (as
> > > > > per Linux specific definitions) are simply dropped, i.e. this isn't related
> > > > > to DisCo for Imaging at all.
> > > >
> > > > So it looks like the changelog of that patch could be improved, right?
> > >
> > > Well, yes. The reason the function is in the file is that nearly all 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 case
> > 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?