Re: [PATCH] ACPI: video: Handle fetching EDID as ACPI_TYPE_PACKAGE

[Mario Limonciello]

On 3/28/2025 13:10, Gergo Koteles wrote:
> Hi Mario,
>
> Thanks for the suggestions!
>
> On Fri, 2025-03-28 at 08:42 -0500, Mario Limonciello wrote:
> > On 3/28/2025 06:12, Rafael J. Wysocki wrote:
> > > CC: Hans
> > >
> > > On Fri, Mar 28, 2025 at 3:51 AM Gergo Koteles <soyer@xxxxxx> wrote:
> > > > Some Lenovo laptops incorrectly return EDID as
> > > > buffer in ACPI package (instead of just a buffer)
> > > > when calling _DDC.
> > > >
> > > > Calling _DDC generates this ACPI Warning:
> > > > ACPI Warning: \_SB.PCI0.GP17.VGA.LCD._DDC: Return type mismatch - \
> > > > found Package, expected Integer/Buffer (20240827/nspredef-254)
> > > >
> > > > Use the first element of the package to get the EDID buffer.
> > > >
> > > > The DSDT:
> > > >
> > > > Name (AUOP, Package (0x01)
> > > > {
> > > >           Buffer (0x80)
> > > >           {
> > > >           ...
> > > >           }
> > > > })
> > > >
> > > > ...
> > > >
> > > > Method (_DDC, 1, NotSerialized)  // _DDC: Display Data Current
> > > > {
> > > >           If ((PAID == AUID))
> > > >           {
> > > >                   Return (AUOP) /* \_SB_.PCI0.GP17.VGA_.LCD_.AUOP */
> > > >           }
> > > >           ElseIf ((PAID == IVID))
> > > >           {
> > > >                   Return (IVOP) /* \_SB_.PCI0.GP17.VGA_.LCD_.IVOP */
> > > >           }
> > > >           ElseIf ((PAID == BOID))
> > > >           {
> > > >                   Return (BOEP) /* \_SB_.PCI0.GP17.VGA_.LCD_.BOEP */
> > > >           }
> > > >           ElseIf ((PAID == SAID))
> > > >           {
> > > >                   Return (SUNG) /* \_SB_.PCI0.GP17.VGA_.LCD_.SUNG */
> > > >           }
> > > >
> > > >           Return (Zero)
> > > > }
> > > >
> > > > Cc: stable@xxxxxxxxxxxxxxx
> > > > Fixes: c6a837088bed ("drm/amd/display: Fetch the EDID from _DDC if available for eDP")
> > > > Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4085
> > > > Signed-off-by: Gergo Koteles <soyer@xxxxxx>
> >
> > FWIW the ACPI spec is clear that this /should/ be an ACPI buffer.
> >
> > https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/Apx_B_Video_Extensions/output-device-specific-methods.html#ddc-return-the-edid-for-this-device
> >
> > That being said this is production firmware and in the wild, I don't
> > personally see a problem with handling it this way.
> >
> > Some other improvement suggestion though below.
> >
> > > > ---
> > > >    drivers/acpi/acpi_video.c | 5 ++++-
> > > >    1 file changed, 4 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
> > > > index efdadc74e3f4..65cf36796506 100644
> > > > --- a/drivers/acpi/acpi_video.c
> > > > +++ b/drivers/acpi/acpi_video.c
> > > > @@ -649,6 +649,9 @@ acpi_video_device_EDID(struct acpi_video_device *device, void **edid, int length
> > > >
> > > >           obj = buffer.pointer;
> > > >
> > > > +       if (obj && obj->type == ACPI_TYPE_PACKAGE && obj->package.count == 1)
> > > > +               obj = &obj->package.elements[0];
> > > > +
> >
> > As the ACPI spec indicates this should be a buffer, I think it's a good
> > idea to emit a FW_BUG message here so that this can be detected by users
> > and tools like FWTS and the firmware can be improved in the future.
> >
> > Something like this:
> >
> > if (condition) {
> > 	pr_info(FW_BUG "EDID was found in ACPI package instead of ACPI buffer");
> > 	obj = &obj->package.elements[0];
> > }
>
> An ACPI Warning is currently being generated:
>
> ACPI Warning: \_SB.PCI0.GP17.VGA.LCD._DDC: Return type mismatch - found
> Package, expected Integer/Buffer (20240827/nspredef-254)
>
> This is also noticed by FWTS in the form of KlogAcpiReturnTypeMismatch
> and may be noticed by users as well.
>
> I think it is unnecessary to emit two warnings for the same problem.
>
> However, some comments could make the code clearer. I will add some
> comments to V2.

Ah yes; if this warning is already being emitted no extra FW_BUG is needed.

Sounds good on comments for v2.

You might also reference the ACPI spec in your commit message in v2.

> > > >           if (obj && obj->type == ACPI_TYPE_BUFFER) {
> > > >                   *edid = kmemdup(obj->buffer.pointer, obj->buffer.length, GFP_KERNEL);
> > > >                   ret = *edid ? obj->buffer.length : -ENOMEM;
> > > > @@ -658,7 +661,7 @@ acpi_video_device_EDID(struct acpi_video_device *device, void **edid, int length
> > > >                   ret = -EFAULT;
> > > >           }
> > > >
> > > > -       kfree(obj);
> > > > +       kfree(buffer.pointer);
> >
> > Any reason for this change?  obj is assigned to buffer.pointer already.
> >
> > >
>
> In the case of an ACPI package, obj points to the first element of the
> package. The buffer.pointer still points to the original location.

Got it thanks.

> Thanks,
> Gergo