[PATCH] drm/amdgpu: Fix incorrect return value in sysfs for pp_od_clk_voltage

[Matt Coffin]

Hi all,

As of 026acaeac2d205f22c0f682cc1c7b1a85b9ccd00 ("drm/amdgpu: revert "fix
system hang issue during GPU reset""), this patch is no longer needed,
and won't apply, because the badly-behaving code was removed; I'll
withdraw this patch for now.

Sorry to those who wasted their time reviewing.

Cheers,
Matt

On 8/13/20 7:15 PM, Matt Coffin wrote:
> The changes in edad8312cbbf9a33c86873fc4093664f150dd5c1 introduced an
> issue with the sysfs interface for pp_od_clk_voltage. It overwrites the
> return value to 0 when it calls another function, then returns 0. The
> intended behavior is that a positive return value indicates the number
> of bytes from the buffer that you processed in that call.
> 
> With the 0 return value, clients would submit the same value to be
> written over and over again, resulting in an infinite loop.
> 
> This is resolved by returning the count of bytes read (in this case the
> whole message), when the desired return is 0 (success).
> 
> Fixes: edad8312cbbf ("drm/amdgpu: fix system hang issue during GPU")
> Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1245
> Signed-off-by: Matt Coffin <mcoffin13 at gmail.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c
> index 1705e328c6fc..f00c7ed361d4 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c
> @@ -937,7 +937,11 @@ static ssize_t amdgpu_set_pp_od_clk_voltage(struct device *dev,
>  
>  pro_end:
>  	up_read(&adev->reset_sem);
> -	return ret;
> +	if (ret) {
> +		return ret;
> +	} else {
> +		return count;
> +	}
>  }
>  
>  static ssize_t amdgpu_get_pp_od_clk_voltage(struct device *dev,
>