[RFC 3/4] accel/ivpu: Remove support for uncached buffers

[Jeffrey Hugo]

On 9/19/2023 3:49 AM, Stanislaw Gruszka wrote:
> On Mon, Sep 11, 2023 at 09:24:42AM -0600, Jeffrey Hugo wrote:
>> On 9/1/2023 10:48 AM, Stanislaw Gruszka wrote:
>>> From: Jacek Lawrynowicz <jacek.lawrynowicz at linux.intel.com>
>>>
>>> Usages of DRM_IVPU_BO_UNCACHED should be replaced by DRM_IVPU_BO_WC.
>>> There is no functional benefit from DRM_IVPU_BO_UNCACHED if these
>>> buffers are never mapped to host VM.
>>>
>>> This allows to cut the buffer handling code in the kernel driver
>>> by half.
>>>
>>> Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz at linux.intel.com>
>>> Signed-off-by: Stanislaw Gruszka <stanislaw.gruszka at linux.intel.com>
>>> ---
>>>    drivers/accel/ivpu/ivpu_fw.c  | 2 +-
>>>    drivers/accel/ivpu/ivpu_gem.c | 3 ---
>>>    include/uapi/drm/ivpu_accel.h | 2 +-
>>>    3 files changed, 2 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/accel/ivpu/ivpu_fw.c b/drivers/accel/ivpu/ivpu_fw.c
>>> index 2fef9fe154aa..8ab0f3225205 100644
>>> --- a/drivers/accel/ivpu/ivpu_fw.c
>>> +++ b/drivers/accel/ivpu/ivpu_fw.c
>>> @@ -248,7 +248,7 @@ static int ivpu_fw_mem_init(struct ivpu_device *vdev)
>>>    	if (fw->shave_nn_size) {
>>>    		fw->mem_shave_nn = ivpu_bo_alloc_internal(vdev, vdev->hw->ranges.shave.start,
>>> -							  fw->shave_nn_size, DRM_IVPU_BO_UNCACHED);
>>> +							  fw->shave_nn_size, DRM_IVPU_BO_WC);
>>>    		if (!fw->mem_shave_nn) {
>>>    			ivpu_err(vdev, "Failed to allocate shavenn buffer\n");
>>>    			ret = -ENOMEM;
>>> diff --git a/drivers/accel/ivpu/ivpu_gem.c b/drivers/accel/ivpu/ivpu_gem.c
>>> index 915c53d7bb97..2a91eb1e3627 100644
>>> --- a/drivers/accel/ivpu/ivpu_gem.c
>>> +++ b/drivers/accel/ivpu/ivpu_gem.c
>>> @@ -89,8 +89,6 @@ static int __must_check shmem_alloc_pages_locked(struct ivpu_bo *bo)
>>>    	if (bo->flags & DRM_IVPU_BO_WC)
>>>    		set_pages_array_wc(pages, npages);
>>> -	else if (bo->flags & DRM_IVPU_BO_UNCACHED)
>>> -		set_pages_array_uc(pages, npages);
>>>    	bo->pages = pages;
>>>    	return 0;
>>> @@ -366,7 +364,6 @@ ivpu_bo_alloc(struct ivpu_device *vdev, u64 size, u32 flags, const struct ivpu_b
>>>    	switch (flags & DRM_IVPU_BO_CACHE_MASK) {
>>>    	case DRM_IVPU_BO_CACHED:
>>> -	case DRM_IVPU_BO_UNCACHED:
>>>    	case DRM_IVPU_BO_WC:
>>>    		break;
>>>    	default:
>>> diff --git a/include/uapi/drm/ivpu_accel.h b/include/uapi/drm/ivpu_accel.h
>>> index 262db0c3beee..de1944e42c65 100644
>>> --- a/include/uapi/drm/ivpu_accel.h
>>> +++ b/include/uapi/drm/ivpu_accel.h
>>> @@ -196,7 +196,7 @@ struct drm_ivpu_bo_create {
>>>    	 *
>>>    	 * %DRM_IVPU_BO_UNCACHED:
>>>    	 *
>>> -	 * Allocated BO will not be cached on host side nor snooped on the VPU side.
>>> +	 * Not supported. Use DRM_IVPU_BO_WC instead.
>>>    	 *
>>>    	 * %DRM_IVPU_BO_WC:
>>>    	 *
>>
>> Feels like this will break existing userspace.  You could see if userspace
>> specified UNCACHED and change it to WC before processing the request.  Maybe
>> also use WARN_ONCE to indicate that userspace should be updated.
>>
>> Or is it the case that userspace never actually used this?
> 
> Usage of those buffers was removed some time ago:
> https://github.com/intel/linux-vpu-driver/commit/c473c9826cb28fa3dcf8883fc804b1e84c6b5fb1
> 
> And will not be part of first user-mode driver release. I think we can
> safely do the change.

Fair enough.  Thanks for the clarification.

Reviewed-by: Jeffrey Hugo <quic_jhugo at quicinc.com>