[PATCH] drm/amd/display: Fix error code on failure to set brightness

[PATCH] drm/amd/display: Fix error code on failure to set brightness

[Anand K Mistry]

The backlight_ops.update_status function is required to return a
negative error code on failure. Returning a positive code may be
interpreted as a success. This is true for the 'brightness' sysfs file,
which passes through a non-zero value as the return value of the write()
syscall. This is interpreted in user-space as a successful write of 1
character, which is obviously wrong.

It's not clear exactly what error code to use, but EINVAL should be
reasonable.

Signed-off-by: Anand K Mistry <amistry@google.com>
---

 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 652cc1a0e450..ad322613390d 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -3431,7 +3431,7 @@ static int amdgpu_dm_backlight_update_status(struct backlight_device *bd)
 	else
 		rc = dc_link_set_backlight_level(dm->backlight_link, brightness, 0);
 
-	return rc ? 0 : 1;
+	return rc ? 0 : -EINVAL;
 }
 
 static int amdgpu_dm_backlight_get_brightness(struct backlight_device *bd)
-- 
2.32.0.rc1.229.g3e70b5a671-goog

Re: [PATCH] drm/amd/display: Fix error code on failure to set brightness

[Harry Wentland]

On 2021-06-08 12:32 a.m., Anand K Mistry wrote:
> The backlight_ops.update_status function is required to return a
> negative error code on failure. Returning a positive code may be
> interpreted as a success. This is true for the 'brightness' sysfs file,
> which passes through a non-zero value as the return value of the write()
> syscall. This is interpreted in user-space as a successful write of 1
> character, which is obviously wrong.
> 
> It's not clear exactly what error code to use, but EINVAL should be
> reasonable.
> 
> Signed-off-by: Anand K Mistry <amistry@google.com>

Thanks for your patch but this code has changed on amd-staging-drm-next.

Can you try with the latest? The new backlight_update_status will always
return 0 now.

Harry

> ---
> 
>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index 652cc1a0e450..ad322613390d 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -3431,7 +3431,7 @@ static int amdgpu_dm_backlight_update_status(struct backlight_device *bd)
>  	else
>  		rc = dc_link_set_backlight_level(dm->backlight_link, brightness, 0);
>  
> -	return rc ? 0 : 1;
> +	return rc ? 0 : -EINVAL;
>  }
>  
>  static int amdgpu_dm_backlight_get_brightness(struct backlight_device *bd)
> 

Re: [PATCH] drm/amd/display: Fix error code on failure to set brightness

[Anand K. Mistry]

>
> Thanks for your patch but this code has changed on amd-staging-drm-next.
>
> Can you try with the latest? The new backlight_update_status will always
> return 0 now.

Perfect! This solves my actual issue which is that restoring the
backlight level is failing on my device. Thank you.


-- 
Anand K. Mistry
Software Engineer
Google Australia