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

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Message-ID: <61c3df83ab73aba0bc7a941a443cd7faf4cf7fb0.1743195250.git.soyer@irl.hu>
Date: Fri, 28 Mar 2025 22:08:56 +0100
From: Gergo Koteles <soyer@....hu>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
  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>,
  Hans de Goede <hdegoede@...hat.com>
Cc: linux-acpi@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
  linux-kernel@...r.kernel.org, Gergo Koteles <soyer@....hu>,
  stable@...r.kernel.org
Subject: [PATCH v2] ACPI: video: Handle fetching EDID as ACPI_TYPE_PACKAGE

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/

 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