[PATCH 1/2] drm/amdgpu: invalidate mmhub semphore workaround in amdgpu_virt

[Christian König]

Hi Changfeng,

[adding Monk and Emily as well].

I thought more about this and came to the conclusion that this won't 
work and might result in a lockup as well.

We are using the KIQ on SRIOV for GPUVM invalidation because we need an 
atomic read/modify/write cycle since we found that the invalidation 
engine is resetted with every world switch.

Now accessing the semaphore registers is not atomic any more and we 
could have a world switch in between grabbing the semaphore and sending 
the VM invalidation. That either won't work or could result in a lockup 
as well.

Question for Emily and Monk: Do we support power gating of the MMHUB 
with SRIOV? I don't think so and when that's correct we could just drop 
this patch.

Regards,
Christian.

Am 20.11.19 um 10:14 schrieb Changfeng.Zhu:
> From: changzhu <Changfeng.Zhu at amd.com>
>
> It may lose gpuvm invalidate acknowldege state across power-gating off
> cycle. To avoid this issue in virt invalidation, add semaphore acquire
> before invalidation and semaphore release after invalidation.
>
> Change-Id: Ie98304e475166b53eed033462d76423b6b0fc25b
> Signed-off-by: changzhu <Changfeng.Zhu at amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c | 26 ++++++++++++++++++++++--
>   drivers/gpu/drm/amd/amdgpu/amdgpu_virt.h |  3 ++-
>   drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c    |  3 ++-
>   3 files changed, 28 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
> index f04eb1a64271..70ffaf91cd12 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
> @@ -135,7 +135,8 @@ void amdgpu_virt_kiq_wreg(struct amdgpu_device *adev, uint32_t reg, uint32_t v)
>   
>   void amdgpu_virt_kiq_reg_write_reg_wait(struct amdgpu_device *adev,
>   					uint32_t reg0, uint32_t reg1,
> -					uint32_t ref, uint32_t mask)
> +					uint32_t ref, uint32_t mask,
> +					uint32_t sem)
>   {
>   	struct amdgpu_kiq *kiq = &adev->gfx.kiq;
>   	struct amdgpu_ring *ring = &kiq->ring;
> @@ -144,9 +145,30 @@ void amdgpu_virt_kiq_reg_write_reg_wait(struct amdgpu_device *adev,
>   	uint32_t seq;
>   
>   	spin_lock_irqsave(&kiq->ring_lock, flags);
> -	amdgpu_ring_alloc(ring, 32);
> +	amdgpu_ring_alloc(ring, 60);
> +
> +	/*
> +	 * It may lose gpuvm invalidate acknowldege state across power-gating
> +	 * off cycle, add semaphore acquire before invalidation and semaphore
> +	 * release after invalidation to avoid entering power gated state
> +	 * to WA the Issue
> +	 */
> +
> +	/* a read return value of 1 means semaphore acuqire */
> +	if (ring->funcs->vmhub == AMDGPU_MMHUB_0 ||
> +	    ring->funcs->vmhub == AMDGPU_MMHUB_1)
> +	amdgpu_ring_emit_reg_wait(ring, sem, 0x1, 0x1);
> +
>   	amdgpu_ring_emit_reg_write_reg_wait(ring, reg0, reg1,
>   					    ref, mask);
> +	/*
> +	 * add semaphore release after invalidation,
> +	 * write with 0 means semaphore release
> +	 */
> +	if (ring->funcs->vmhub == AMDGPU_MMHUB_0 ||
> +	    ring->funcs->vmhub == AMDGPU_MMHUB_1)
> +	amdgpu_ring_emit_wreg(ring, sem, 0);
> +
>   	amdgpu_fence_emit_polling(ring, &seq);
>   	amdgpu_ring_commit(ring);
>   	spin_unlock_irqrestore(&kiq->ring_lock, flags);
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.h
> index b0b2bdc750df..bda6a2f37dc0 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.h
> @@ -295,7 +295,8 @@ uint32_t amdgpu_virt_kiq_rreg(struct amdgpu_device *adev, uint32_t reg);
>   void amdgpu_virt_kiq_wreg(struct amdgpu_device *adev, uint32_t reg, uint32_t v);
>   void amdgpu_virt_kiq_reg_write_reg_wait(struct amdgpu_device *adev,
>   					uint32_t reg0, uint32_t rreg1,
> -					uint32_t ref, uint32_t mask);
> +					uint32_t ref, uint32_t mask,
> +					uint32_t sem);
>   int amdgpu_virt_request_full_gpu(struct amdgpu_device *adev, bool init);
>   int amdgpu_virt_release_full_gpu(struct amdgpu_device *adev, bool init);
>   int amdgpu_virt_reset_gpu(struct amdgpu_device *adev);
> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c b/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
> index f25cd97ba5f2..1ae59af7836a 100644
> --- a/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
> +++ b/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
> @@ -448,9 +448,10 @@ static void gmc_v9_0_flush_gpu_tlb(struct amdgpu_device *adev, uint32_t vmid,
>   			!adev->in_gpu_reset) {
>   		uint32_t req = hub->vm_inv_eng0_req + eng;
>   		uint32_t ack = hub->vm_inv_eng0_ack + eng;
> +		uint32_t sem = hub->vm_inv_eng0_sem + eng;
>   
>   		amdgpu_virt_kiq_reg_write_reg_wait(adev, req, ack, tmp,
> -				1 << vmid);
> +						   1 << vmid, sem);
>   		return;
>   	}
>