On 10/10/2025 11:11, Boris Brezillon wrote:
> From: Loïc Molinari <[email protected]>
>
> Will be used by the UMD to optimize CPU accesses to buffers
> that are frequently read by the CPU, or on which the access
> pattern makes non-cacheable mappings inefficient.
>
> Mapping buffers CPU-cached implies taking care of the CPU
> cache maintenance in the UMD, unless the GPU is IO coherent.
>
> v2:
> - Add more to the commit message
> - Tweak the doc
> - Make sure we sync the section of the BO pointing to the CS
> syncobj before we read its seqno
>
> Signed-off-by: Loïc Molinari <[email protected]>
> Signed-off-by: Boris Brezillon <[email protected]>
> ---
> drivers/gpu/drm/panthor/panthor_drv.c | 8 +++++++-
> drivers/gpu/drm/panthor/panthor_gem.c | 3 +++
> drivers/gpu/drm/panthor/panthor_sched.c | 18 ++++++++++++++++--
> include/uapi/drm/panthor_drm.h | 9 +++++++++
> 4 files changed, 35 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c
> b/drivers/gpu/drm/panthor/panthor_drv.c
> index 9004d0ba0e45..af9b431255a4 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -900,7 +900,8 @@ static int panthor_ioctl_vm_destroy(struct drm_device
> *ddev, void *data,
> return panthor_vm_pool_destroy_vm(pfile->vms, args->id);
> }
>
> -#define PANTHOR_BO_FLAGS DRM_PANTHOR_BO_NO_MMAP
> +#define PANTHOR_BO_FLAGS (DRM_PANTHOR_BO_NO_MMAP | \
> + DRM_PANTHOR_BO_WB_MMAP)
>
> static int panthor_ioctl_bo_create(struct drm_device *ddev, void *data,
> struct drm_file *file)
> @@ -919,6 +920,10 @@ static int panthor_ioctl_bo_create(struct drm_device
> *ddev, void *data,
> goto out_dev_exit;
> }
>
> + if ((args->flags & DRM_PANTHOR_BO_NO_MMAP) &&
> + (args->flags & DRM_PANTHOR_BO_WB_MMAP))
> + return -EINVAL;
> +
> if (args->exclusive_vm_id) {
> vm = panthor_vm_pool_get_vm(pfile->vms, args->exclusive_vm_id);
> if (!vm) {
> @@ -1450,6 +1455,7 @@ static int panthor_ioctl_bo_query_info(struct
> drm_device *ddev, void *data,
> return -ENOENT;
>
> bo = to_panthor_bo(obj);
> +
NIT: Stray newline added.
> args->pad = 0;
> args->create_flags = bo->flags;
>
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c
> b/drivers/gpu/drm/panthor/panthor_gem.c
> index 617e04134d30..a0ccc316e375 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.c
> +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> @@ -280,6 +280,9 @@ panthor_gem_create_with_handle(struct drm_file *file,
> bo = to_panthor_bo(&shmem->base);
> bo->flags = flags;
>
> + if (flags & DRM_PANTHOR_BO_WB_MMAP)
> + shmem->map_wc = false;
> +
> if (exclusive_vm) {
> bo->exclusive_vm_root_gem = panthor_vm_root_gem(exclusive_vm);
> drm_gem_object_get(bo->exclusive_vm_root_gem);
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c
> b/drivers/gpu/drm/panthor/panthor_sched.c
> index 0cc9055f4ee5..5f9dba3a9d65 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.c
> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> @@ -868,8 +868,11 @@ panthor_queue_get_syncwait_obj(struct panthor_group
> *group, struct panthor_queue
> struct iosys_map map;
> int ret;
>
> - if (queue->syncwait.kmap)
> - return queue->syncwait.kmap + queue->syncwait.offset;
> + if (queue->syncwait.kmap) {
> + bo = container_of(queue->syncwait.obj,
> + struct panthor_gem_object, base.base);
> + goto out_sync;
> + }
>
> bo = panthor_vm_get_bo_for_va(group->vm,
> queue->syncwait.gpu_va,
> @@ -886,6 +889,17 @@ panthor_queue_get_syncwait_obj(struct panthor_group
> *group, struct panthor_queue
> if (drm_WARN_ON(&ptdev->base, !queue->syncwait.kmap))
> goto err_put_syncwait_obj;
>
> +out_sync:
> + /* Make sure the CPU caches are invalidated before the seqno is read.
> + * drm_gem_shmem_sync() is a NOP if wap_wc=false, so no need to check
NIT: s/wap_wc/map_wc
> + * it here.
> + */
> + drm_gem_shmem_sync(&bo->base, queue->syncwait.offset,
> + queue->syncwait.sync64 ?
> + sizeof(struct panthor_syncobj_64b) :
> + sizeof(struct panthor_syncobj_32b),
> + DRM_GEM_OBJECT_CPU_ACCESS |
> DRM_GEM_OBJECT_READ_ACCESS);
> +
> return queue->syncwait.kmap + queue->syncwait.offset;
>
> err_put_syncwait_obj:
> diff --git a/include/uapi/drm/panthor_drm.h b/include/uapi/drm/panthor_drm.h
> index 54502286c8b1..e77d65e51c64 100644
> --- a/include/uapi/drm/panthor_drm.h
> +++ b/include/uapi/drm/panthor_drm.h
> @@ -681,6 +681,15 @@ struct drm_panthor_vm_get_state {
> enum drm_panthor_bo_flags {
> /** @DRM_PANTHOR_BO_NO_MMAP: The buffer object will never be CPU-mapped
> in userspace. */
> DRM_PANTHOR_BO_NO_MMAP = (1 << 0),
> +
> + /**
> + * @DRM_PANTHOR_BO_WB_MMAP: Force "Write-Back Cacheable" CPU mapping.
> + *
> + * CPU map the buffer object in userspace by forcing the "Write-Back
> + * Cacheable" cacheability attribute. The mapping otherwise uses the
> + * "Non-Cacheable" attribute if the GPU is not IO coherent.
> + */
> + DRM_PANTHOR_BO_WB_MMAP = (1 << 1),
> };
>
> /**
