[PATCH] drm/amdgpu: remove unsafe optimization to drop preamble ib

[Christian König]

Am 13.05.21 um 05:21 schrieb Jiansong Chen:
> Take the situation with gfxoff, the optimization may cause
> corrupt CE ram contents. In addition emit_cntxcntl callback
> has similar optimization which firmware can handle properly
> even for power feature.

NAK, it is the whole purpose of the preamble IB to be dropped if there 
isn't a context switch.

You are completely disabling this feature with that.

Christian.

>
> Signed-off-by: Jiansong Chen <Jiansong.Chen at amd.com>
> Change-Id: I962946557108bb0575f8b2afc25b18a6dcf0d838
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c | 11 +----------
>   1 file changed, 1 insertion(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
> index 2e6789a7dc46..77baf9b48d67 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
> @@ -130,7 +130,7 @@ int amdgpu_ib_schedule(struct amdgpu_ring *ring, unsigned num_ibs,
>   	struct amdgpu_device *adev = ring->adev;
>   	struct amdgpu_ib *ib = &ibs[0];
>   	struct dma_fence *tmp = NULL;
> -	bool skip_preamble, need_ctx_switch;
> +	bool need_ctx_switch;
>   	unsigned patch_offset = ~0;
>   	struct amdgpu_vm *vm;
>   	uint64_t fence_ctx;
> @@ -227,7 +227,6 @@ int amdgpu_ib_schedule(struct amdgpu_ring *ring, unsigned num_ibs,
>   	if (need_ctx_switch)
>   		status |= AMDGPU_HAVE_CTX_SWITCH;
>   
> -	skip_preamble = ring->current_ctx == fence_ctx;
>   	if (job && ring->funcs->emit_cntxcntl) {
>   		status |= job->preamble_status;
>   		status |= job->preemption_status;
> @@ -245,14 +244,6 @@ int amdgpu_ib_schedule(struct amdgpu_ring *ring, unsigned num_ibs,
>   	for (i = 0; i < num_ibs; ++i) {
>   		ib = &ibs[i];
>   
> -		/* drop preamble IBs if we don't have a context switch */
> -		if ((ib->flags & AMDGPU_IB_FLAG_PREAMBLE) &&
> -		    skip_preamble &&
> -		    !(status & AMDGPU_PREAMBLE_IB_PRESENT_FIRST) &&
> -		    !amdgpu_mcbp &&
> -		    !amdgpu_sriov_vf(adev)) /* for SRIOV preemption, Preamble CE ib must be inserted anyway */
> -			continue;
> -
>   		if (job && ring->funcs->emit_frame_cntl) {
>   			if (secure != !!(ib->flags & AMDGPU_IB_FLAGS_SECURE)) {
>   				amdgpu_ring_emit_frame_cntl(ring, false, secure);