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Date: Wed, 12 Jun 2024 19:06:51 +0000
From: Sakari Ailus <sakari.ailus@linux.intel.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Hans de Goede <hdegoede@redhat.com>, Genes Lists <lists@sapience.com>,
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	"regressions@lists.linux.dev" <regressions@lists.linux.dev>
Subject: Re: [PATCH 1/1] ACPI: scan: Ignore Dell XPS 9320 camera graph port
 nodes
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Hi Rafael,

On Wed, Jun 12, 2024 at 08:41:43PM +0200, Rafael J. Wysocki wrote:
> Hi Sakari,
> 
> On Wed, Jun 12, 2024 at 8:33 PM Sakari Ailus
> <sakari.ailus@linux.intel.com> wrote:
> >
> > Hi Rafael,
> >
> > On Wed, Jun 12, 2024 at 05:26:46PM +0200, Rafael J. Wysocki wrote:
> > > Hi,
> > >
> > > On Wed, Jun 12, 2024 at 4:30 PM Hans de Goede <hdegoede@redhat.com> wrote:
> > > >
> > > > Hi,
> > > >
> > > > On 6/12/24 3:06 PM, Rafael J. Wysocki wrote:
> > > > > Hi Sakari,
> > > > >
> > > > > On Wed, Jun 12, 2024 at 2:47 PM Sakari Ailus
> > > > > <sakari.ailus@linux.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?
> > > >
> > > > 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 windows
> > > > 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% functional
> > > > ACPI MIPI information. I believe that some work is in place to get correct
> > > > 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 BIOS
> > > > version with which current Windows models are shipping. It is being fixed
> > > > for systems which have Linux support from the vendor but I suspect that
> > > > 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 devices
> > > > going forward. We really need to have 1 reliable source of truth here and
> > > > using information which is ignored by Windows does not seem like the best
> > > > source to use.
> > > >
> > > > Sakari I know you have been pushing for MIPI camera descriptions under
> > > > ACPI to move to a standardized format and I can see how that is a good
> > > > thing, but atm it seems to mainly cause things to break and before
> > > > the ACPI MIPI DISCO support landed in 6.8 we did not have these issues,
> > > > since the information used by the ipu-bridge code does seem to be correct.
> > >
> > > Well, if Windows doesn't use this information, it is almost guaranteed
> > > to be garbage.
> >
> > No ACPI DSDT in production systems uses DisCo for Imaging as of now at
> > least to my knowledge.
> >
> > >
> > > So maybe it would be better to make acpi_graph_ignore_port() return
> > > true by default and false only when the information is known to be
> > > valid.  IOW, whitelist things instead of adding blacklist entries in
> > > perpetuum.
> >
> > What could be gained from this?
> 
> Generally speaking, fewer headaches for people trying to support Linux
> on Intel client platforms.

I don't think that is the case here.

I'd like to reiterate that none of the issues there have been so far
(including with Dell laptops) have been related to DisCo for Imaging.

> 
> Every system that needs to be put into dmi_ignore_port_nodes[] means a
> boot problem for someone that needs to be addressed.
> 
> And after the Hans' patch at
> 
> https://patchwork.kernel.org/project/linux-acpi/patch/20240612104220.22219-1-hdegoede@redhat.com/
> 
> we would effectively get very close to that point anyway.

Dell systems only, and of a limited range.

> 
> Are the ACPI tables on MTL and beyond going to be fixed?  If not,
> we'll probably need to add MTL to the list of platform IDs and so on.
> In what way is this better?

This will very probably take place post-MTL.

-- 
Kind regards,

Sakari Ailus