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

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Date: Fri, 2 Feb 2024 10:09:38 -0600
From: Mario Limonciello <mario.limonciello@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: amd-gfx@...ts.freedesktop.org, Alex Deucher <alexander.deucher@....com>,
 Harry Wentland <harry.wentland@....com>, Hans de Goede
 <hdegoede@...hat.com>, "open list:ACPI" <linux-acpi@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>,
 "open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
 Melissa Wen <mwen@...lia.com>, Mark Pearson <mpearson-lenovo@...ebb.ca>
Subject: Re: [PATCH v3 1/5] ACPI: video: Handle fetching EDID that is longer
 than 256 bytes

On 2/2/2024 10:07, Rafael J. Wysocki wrote:
> On Thu, Feb 1, 2024 at 11:11 PM Mario Limonciello
> <mario.limonciello@....com> 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@....com>
> 
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> 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
>>