[PATCH v3] drm/amdgpu: Fix missing comment for mb() in 'amdgpu_device_aper_access'

[Lazar, Lijo]

On 8/9/2023 11:16 AM, Srinivasan Shanmugam wrote:
> This patch adds the missing code comment for memory barrier
> 
> WARNING: memory barrier without comment
> +                       mb();
> 
> WARNING: memory barrier without comment
> +                       mb();
> 
> Cc: Guchun Chen <guchun.chen at amd.com>
> Cc: Christian König <christian.koenig at amd.com>
> Cc: Alex Deucher <alexander.deucher at amd.com>
> Cc: "Pan, Xinhui" <Xinhui.Pan at amd.com>
> Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam at amd.com>
> ---
> v3:
> 
> Corrected title message
> 
>   drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> index 4f818f13dc9d..bb65e12ed027 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> @@ -305,10 +305,17 @@ size_t amdgpu_device_aper_access(struct amdgpu_device *adev, loff_t pos,
>   
>   		if (write) {
>   			memcpy_toio(addr, buf, count);
> +			/* Make sure contents of system memory are copied/flushed
> +			 * without messing up order of writes to PCI device I/O memory
> +			 */
Make sure HDP write cache flush happens after the memory contents are 
sent over PCIe.

>   			mb();
>   			amdgpu_device_flush_hdp(adev, NULL);
>   		} else {
>   			amdgpu_device_invalidate_hdp(adev, NULL);
> +			/* Make sure contents of system memory drained/invalidated
Similarly, make sure HDP read cache is invalidated before issuing a read 
to the device. No reordering in both cases.

Thanks,
Lijo

> +			 * before copying contents from PCI device I/O memory
> +			 * to system memory
> +			 */
>   			mb();
>   			memcpy_fromio(buf, addr, count);
>   		}