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

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Message-ID: <d3dfe61a-1d4d-4aa6-870c-61249799e6da@redhat.com>
Date: Mon, 31 Mar 2025 15:03:52 +0200
From: Hans de Goede <hdegoede@...hat.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>, Gergo Koteles <soyer@....hu>
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

Hi,

On 31-Mar-25 1:46 PM, Rafael J. Wysocki wrote:
> 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?

No the patch looks good to me:

Reviewed-by: Hans de Goede <hdegoede@...hat.com>

Regards,

Hans




> 
>>  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
>>
>