On Fri, Mar 28, 2025 at 10:09 PM Gergo Koteles <so...@irl.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: sta...@vger.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 <so...@irl.hu>
> ---
> Changes in v2:
> - Added comment
> - Improved commit message
> - Link to v1:
> https://lore.kernel.org/all/4cef341fdf7a0e877c50b502fc95ee8be28aa811.1743129387.git.so...@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
>
