Re: [PATCH] drm/amdgpu: add ih call to process until checkpoint

[Andrey Grodzovsky <andrey.grodzovsky@amd.com>]

On 2021-02-23 4:10 p.m., Jonathan Kim wrote:
> Add IH function to allow caller to process ring entries until the
> checkpoint write pointer.
>
> Suggested-by: Felix Kuehling <felix.kuehling@amd.com>
> Signed-off-by: Jonathan Kim <jonathan.kim@amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ih.c | 46 +++++++++++++++++++++++++-
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ih.h |  2 ++
>   2 files changed, 47 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.c
> index dc852af4f3b7..cae50af9559d 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.c
> @@ -22,7 +22,7 @@
>    */
>   
>   #include <linux/dma-mapping.h>
> -
> +#include <linux/processor.h>
>   #include "amdgpu.h"
>   #include "amdgpu_ih.h"
>   
> @@ -160,6 +160,50 @@ void amdgpu_ih_ring_write(struct amdgpu_ih_ring *ih, const uint32_t *iv,
>   	}
>   }
>   
> +/**
> + * amdgpu_ih_wait_on_checkpoint_process - wait to process IVs up to checkpoint
> + *
> + * @adev: amdgpu_device pointer
> + * @ih: ih ring to process
> + *
> + * Used to ensure ring has processed IVs up to the checkpoint write pointer.
> + */
> +int amdgpu_ih_wait_on_checkpoint_process(struct amdgpu_device *adev,
> +					struct amdgpu_ih_ring *ih)
> +{
> +	u32 prev_rptr, cur_rptr, checkpoint_wptr;
> +
> +	if (!ih->enabled || adev->shutdown)
> +		return -ENODEV;
> +
> +	cur_rptr = READ_ONCE(ih->rptr);
> +	/* Order read of current rptr with checktpoint wptr. */
> +	mb();
> +	checkpoint_wptr = amdgpu_ih_get_wptr(adev, ih);
> +


Isn't rmb() enough in this case ? If I understand correctly you just 
want to confirm that
you are not reading stale checkpoint_wptr while reading fresh cur_rptr.

Andrey


> +	/* allow rptr to wrap around  */
> +	if (cur_rptr > checkpoint_wptr) {
> +		spin_begin();
> +		do {
> +			spin_cpu_relax();
> +			prev_rptr = cur_rptr;
> +			cur_rptr = READ_ONCE(ih->rptr);
> +		} while (cur_rptr >= prev_rptr);
> +		spin_end();
> +	}
> +
> +	/* wait for rptr to catch up to or pass checkpoint. */
> +	spin_begin();
> +	do {
> +		spin_cpu_relax();
> +		prev_rptr = cur_rptr;
> +		cur_rptr = READ_ONCE(ih->rptr);
> +	} while (cur_rptr >= prev_rptr && cur_rptr < checkpoint_wptr);
> +	spin_end();
> +
> +	return 0;
> +}
> +
>   /**
>    * amdgpu_ih_process - interrupt handler
>    *
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.h
> index 6ed4a85fc7c3..6817f0a812d2 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.h
> @@ -87,6 +87,8 @@ int amdgpu_ih_ring_init(struct amdgpu_device *adev, struct amdgpu_ih_ring *ih,
>   void amdgpu_ih_ring_fini(struct amdgpu_device *adev, struct amdgpu_ih_ring *ih);
>   void amdgpu_ih_ring_write(struct amdgpu_ih_ring *ih, const uint32_t *iv,
>   			  unsigned int num_dw);
> +int amdgpu_ih_wait_on_checkpoint_process(struct amdgpu_device *adev,
> +					struct amdgpu_ih_ring *ih);
>   int amdgpu_ih_process(struct amdgpu_device *adev, struct amdgpu_ih_ring *ih);
>   void amdgpu_ih_decode_iv_helper(struct amdgpu_device *adev,
>   				struct amdgpu_ih_ring *ih,
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