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

[Jeffrey Hugo]

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?