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

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On 9/1/2023 10:48 AM, Stanislaw Gruszka wrote:
From: Jacek Lawrynowicz <jacek.lawrynowicz@xxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxx>
Signed-off-by: Stanislaw Gruszka <stanislaw.gruszka@xxxxxxxxxxxxxxx>
---
  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?



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