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];
}
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.
return ret;
}
--
2.49.0
