linux-kernel - Re: [PATCH v2] ACPI: video: Handle fetching EDID as ACPI_TYPE

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Message-ID: <CAJZ5v0jBONZ7UFL0HCOV=7xmnUphL_UTV=_1PnYmR6n0oN4pcg@mail.gmail.com>
Date: Mon, 31 Mar 2025 13:46:10 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Gergo Koteles <soyer@....hu>, Hans de Goede <hdegoede@...hat.com>
Cc: Len Brown <lenb@...nel.org>, Alex Hung <alex.hung@....com>, 
	Mario Limonciello <mario.limonciello@....com>, Rodrigo Siqueira <siqueira@...lia.com>, 
	Alex Deucher <alexander.deucher@....com>, linux-acpi@...r.kernel.org, 
	amd-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] ACPI: video: Handle fetching EDID as ACPI_TYPE_PACKAGE

On Fri, Mar 28, 2025 at 10:09 PM Gergo Koteles <soyer@....hu> wrote:
>
> The _DDC method should return a buffer, or an integer in case of an error.
> But some Lenovo laptops incorrectly return EDID as buffer in ACPI package.
>
> 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)
> }
>
> Link: 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
> Cc: stable@...r.kernel.org
> 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@....hu>
> ---
> Changes in v2:
>  - Added comment
>  - Improved commit message
>  - Link to v1: https://lore.kernel.org/all/4cef341fdf7a0e877c50b502fc95ee8be28aa811.1743129387.git.soyer@irl.hu/

Hans, any concerns here?

>  drivers/acpi/acpi_video.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
> index efdadc74e3f4..103f29661576 100644
> --- a/drivers/acpi/acpi_video.c
> +++ b/drivers/acpi/acpi_video.c
> @@ -649,6 +649,13 @@ acpi_video_device_EDID(struct acpi_video_device *device, void **edid, int length
>
>         obj = buffer.pointer;
>
> +       /*
> +        * Some buggy implementations incorrectly return the EDID buffer in an ACPI package.
> +        * In this case, extract the buffer from the package.
> +        */
> +       if (obj && obj->type == ACPI_TYPE_PACKAGE && obj->package.count == 1)
> +               obj = &obj->package.elements[0];
> +
>         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 +665,7 @@ acpi_video_device_EDID(struct acpi_video_device *device, void **edid, int length
>                 ret = -EFAULT;
>         }
>
> -       kfree(obj);
> +       kfree(buffer.pointer);
>         return ret;
>  }
>
> --
> 2.49.0
>