diff mbox series

[1/2] ACPI: video: Handle fetching EDID that is longer than 256 bytes

Message ID 20240126184639.8187-2-mario.limonciello@amd.com (mailing list archive)
State New, archived
Headers show
Series Fetch EDID from ACPI _DDC method if available | expand

Commit Message

Mario Limonciello Jan. 26, 2024, 6:46 p.m. UTC
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@amd.com>
---
 drivers/acpi/acpi_video.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

Comments

Rafael J. Wysocki Jan. 29, 2024, 1:54 p.m. UTC | #1
On Fri, Jan 26, 2024 at 7:55 PM Mario Limonciello
<mario.limonciello@amd.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.
>
> 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@amd.com>
> ---
>  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.

>         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;
> --
Mario Limonciello Jan. 29, 2024, 4:12 p.m. UTC | #2
On 1/29/2024 07:54, Rafael J. Wysocki wrote:
> On Fri, Jan 26, 2024 at 7:55 PM Mario Limonciello
> <mario.limonciello@amd.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.
>>
>> 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@amd.com>
>> ---
>>   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;
>> --
diff mbox series

Patch

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;
 	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) {
+				length -= 128;
+				status = acpi_video_device_EDID(video_device, &buffer,
+								length);
+				if (ACPI_FAILURE(status) || !buffer ||
+				    buffer->type != ACPI_TYPE_BUFFER) {
+					continue;
+				}
+				break;
 			}
+			if (!length)
+				continue;
 		}
 
 		*edid = buffer->buffer.pointer;