Re: [PATCH v3 1/5] ACPI: video: Handle fetching EDID that is longer than 256 bytes

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On 2/2/2024 10:07, Rafael J. Wysocki wrote:
On Thu, Feb 1, 2024 at 11:11 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.

As _DDC is now called up to 4 times on a machine debugging messages
are noisier than necessary.  Decrease from info to debug.

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>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

or I can apply it if that's preferred.

Thanks!

I think go ahead and apply this one to your -next tree.

The rest might take a few weeks to get right and no need to block on this.


Thanks!

---
v1->v2:
  * Use for loop for acpi_video_get_edid()
  * Use one of Rafael's suggestions for acpi_video_device_EDID()
  * Decrease message level too
---
  drivers/acpi/acpi_video.c | 25 +++++++++----------------
  1 file changed, 9 insertions(+), 16 deletions(-)

diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index 4afdda9db019..3bfd013e09d2 100644
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -625,12 +625,9 @@ acpi_video_device_EDID(struct acpi_video_device *device,

         if (!device)
                 return -ENODEV;
-       if (length == 128)
-               arg0.integer.value = 1;
-       else if (length == 256)
-               arg0.integer.value = 2;
-       else
+       if (!length || (length % 128))
                 return -EINVAL;
+       arg0.integer.value = length / 128;

         status = acpi_evaluate_object(device->dev->handle, "_DDC", &args, &buffer);
         if (ACPI_FAILURE(status))
@@ -641,7 +638,8 @@ acpi_video_device_EDID(struct acpi_video_device *device,
         if (obj && obj->type == ACPI_TYPE_BUFFER)
                 *edid = obj;
         else {
-               acpi_handle_info(device->dev->handle, "Invalid _DDC data\n");
+               acpi_handle_debug(device->dev->handle,
+                                "Invalid _DDC data for length %ld\n", length);
                 status = -EFAULT;
                 kfree(obj);
         }
@@ -1447,7 +1445,6 @@ 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;

                 if (!video_device)
                         continue;
@@ -1478,18 +1475,14 @@ int acpi_video_get_edid(struct acpi_device *device, int type, int device_id,
                         continue;
                 }

-               status = acpi_video_device_EDID(video_device, &buffer, length);
-
-               if (ACPI_FAILURE(status) || !buffer ||
-                   buffer->type != ACPI_TYPE_BUFFER) {
-                       length = 128;
+               for (length = 512; length > 0; length -= 128) {
                         status = acpi_video_device_EDID(video_device, &buffer,
                                                         length);
-                       if (ACPI_FAILURE(status) || !buffer ||
-                           buffer->type != ACPI_TYPE_BUFFER) {
-                               continue;
-                       }
+                       if (ACPI_SUCCESS(status))
+                               break;
                 }
+               if (!length)
+                       continue;

                 *edid = buffer->buffer.pointer;
                 return length;
--
2.34.1





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