On 1/29/2024 07:54, Rafael J. Wysocki wrote:
On Fri, Jan 26, 2024 at 7:55 PM Mario Limonciello
<mario.limonciello@xxxxxxx> wrote:
The ACPI specification allows for an EDID to be up to 512 bytes but
the _DDC EDID fetching code will only try up to 256 bytes.
Modify the code to instead start at 512 bytes and work it's way
down instead.
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
Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
---
drivers/acpi/acpi_video.c | 23 ++++++++++++++++-------
1 file changed, 16 insertions(+), 7 deletions(-)
diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index 62f4364e4460..b3b15dd4755d 100644
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -624,6 +624,10 @@ acpi_video_device_EDID(struct acpi_video_device *device,
arg0.integer.value = 1;
else if (length == 256)
arg0.integer.value = 2;
+ else if (length == 384)
+ arg0.integer.value = 3;
+ else if (length == 512)
+ arg0.integer.value = 4;
It looks like switch () would be somewhat better.
Or maybe even
arg0.integer.value = length / 128;
The validation could be added too:
if (arg0.integer.value > 4 || arg0.integer.value * 128 != length)
return -EINVAL;
but it is pointless, because the caller is never passing an invalid
number to it AFAICS.
Thanks. I'll swap over to one of these suggestions.
I will also split this patch separately from the other as the other will
take some time with refactoring necessary in DRM that will take a cycle
or two.
else
return -EINVAL;
@@ -1443,7 +1447,7 @@ int acpi_video_get_edid(struct acpi_device *device, int type, int device_id,
for (i = 0; i < video->attached_count; i++) {
video_device = video->attached_array[i].bind_info;
- length = 256;
+ length = 512;
if (!video_device)
continue;
@@ -1478,13 +1482,18 @@ int acpi_video_get_edid(struct acpi_device *device, int type, int device_id,
if (ACPI_FAILURE(status) || !buffer ||
buffer->type != ACPI_TYPE_BUFFER) {
- length = 128;
- status = acpi_video_device_EDID(video_device, &buffer,
- length);
- if (ACPI_FAILURE(status) || !buffer ||
- buffer->type != ACPI_TYPE_BUFFER) {
- continue;
+ while (length) {
I would prefer a do {} while () loop here, which could include the
first invocation of acpi_video_device_EDID() too (and reduce code
duplication a bit).
+ length -= 128;
+ status = acpi_video_device_EDID(video_device, &buffer,
+ length);
No line break, please.
+ if (ACPI_FAILURE(status) || !buffer ||
+ buffer->type != ACPI_TYPE_BUFFER) {
+ continue;
+ }
+ break;
}
+ if (!length)
+ continue;
}
*edid = buffer->buffer.pointer;
--
