[PATCH v3 1/3] drm: Add support for GEM buffers backed by non-coherent memory
Thomas Zimmermann
tzimmermann at suse.de
Sat May 15 09:03:34 UTC 2021
Hi
Am 14.05.21 um 22:11 schrieb Paul Cercueil:
> Having GEM buffers backed by non-coherent memory is interesting in the
> particular case where it is faster to render to a non-coherent buffer
> then sync the data cache, than to render to a write-combine buffer, and
> (by extension) much faster than using a shadow buffer. This is true for
> instance on some Ingenic SoCs, where even simple blits (e.g. memcpy)
> are about three times faster using this method.
>
> Add a 'map_noncoherent' flag to the drm_gem_cma_object structure, which
> can be set by the drivers when they create the dumb buffer.
>
> Since this really only applies to software rendering, disable this flag
> as soon as the CMA objects are exported via PRIME.
>
> v3: New patch. Now uses a simple 'map_noncoherent' flag to control how
> the objects are mapped, and use the new dma_mmap_pages function.
>
> Signed-off-by: Paul Cercueil <paul at crapouillou.net>
> ---
> drivers/gpu/drm/drm_gem_cma_helper.c | 41 +++++++++++++++++++++++++---
> include/drm/drm_gem_cma_helper.h | 7 ++++-
> 2 files changed, 43 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c
> index 7942cf05cd93..81a31bcf7d68 100644
> --- a/drivers/gpu/drm/drm_gem_cma_helper.c
> +++ b/drivers/gpu/drm/drm_gem_cma_helper.c
> @@ -115,8 +115,15 @@ struct drm_gem_cma_object *drm_gem_cma_create(struct drm_device *drm,
> if (IS_ERR(cma_obj))
> return cma_obj;
>
> - cma_obj->vaddr = dma_alloc_wc(drm->dev, size, &cma_obj->paddr,
> - GFP_KERNEL | __GFP_NOWARN);
> + if (cma_obj->map_noncoherent) {
> + cma_obj->vaddr = dma_alloc_noncoherent(drm->dev, size,
> + &cma_obj->paddr,
> + DMA_TO_DEVICE,
> + GFP_KERNEL | __GFP_NOWARN);
> + } else {
> + cma_obj->vaddr = dma_alloc_wc(drm->dev, size, &cma_obj->paddr,
> + GFP_KERNEL | __GFP_NOWARN);
> + }
> if (!cma_obj->vaddr) {
> drm_dbg(drm, "failed to allocate buffer with size %zu\n",
> size);
> @@ -499,8 +506,13 @@ int drm_gem_cma_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
>
> cma_obj = to_drm_gem_cma_obj(obj);
>
> - ret = dma_mmap_wc(cma_obj->base.dev->dev, vma, cma_obj->vaddr,
> - cma_obj->paddr, vma->vm_end - vma->vm_start);
> + vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
> + if (!cma_obj->map_noncoherent)
> + vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
> +
> + ret = dma_mmap_pages(cma_obj->base.dev->dev,
> + vma, vma->vm_end - vma->vm_start,
> + virt_to_page(cma_obj->vaddr));
> if (ret)
> drm_gem_vm_close(vma);
>
> @@ -556,3 +568,24 @@ drm_gem_cma_prime_import_sg_table_vmap(struct drm_device *dev,
> return obj;
> }
> EXPORT_SYMBOL(drm_gem_cma_prime_import_sg_table_vmap);
> +
> +/**
> + * drm_gem_cma_prime_mmap - PRIME mmap function for CMA GEM drivers
> + * @obj: GEM object
> + * @vma: Virtual address range
> + *
> + * Carbon copy of drm_gem_prime_mmap, but the 'map_noncoherent' flag is
> + * disabled to ensure that the exported buffers have the expected cache
> + * coherency.
> + */
> +int drm_gem_cma_prime_mmap(struct drm_gem_object *obj,
> + struct vm_area_struct *vma)
> +{
> + struct drm_gem_cma_object *cma_obj = to_drm_gem_cma_obj(obj);
> +
> + /* Use standard cache settings for PRIME-exported GEM buffers */
> + cma_obj->map_noncoherent = false;
> +
> + return drm_gem_prime_mmap(obj, vma);
> +}
> +EXPORT_SYMBOL(drm_gem_cma_prime_mmap);
> diff --git a/include/drm/drm_gem_cma_helper.h b/include/drm/drm_gem_cma_helper.h
> index 0a9711caa3e8..b597e00fd5f6 100644
> --- a/include/drm/drm_gem_cma_helper.h
> +++ b/include/drm/drm_gem_cma_helper.h
> @@ -16,6 +16,7 @@ struct drm_mode_create_dumb;
> * more than one entry but they are guaranteed to have contiguous
> * DMA addresses.
> * @vaddr: kernel virtual address of the backing memory
> + * @map_noncoherent: if true, the GEM object is backed by non-coherent
memory
> */
> struct drm_gem_cma_object {
> struct drm_gem_object base;
> @@ -24,6 +25,8 @@ struct drm_gem_cma_object {
>
> /* For objects with DMA memory allocated by GEM CMA */
> void *vaddr;
> +
> + bool map_noncoherent;
> };
>
> #define to_drm_gem_cma_obj(gem_obj) \
> @@ -119,7 +122,7 @@ int drm_gem_cma_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma);
> .prime_handle_to_fd = drm_gem_prime_handle_to_fd, \
> .prime_fd_to_handle = drm_gem_prime_fd_to_handle, \
> .gem_prime_import_sg_table = drm_gem_cma_prime_import_sg_table, \
> - .gem_prime_mmap = drm_gem_prime_mmap
> + .gem_prime_mmap = drm_gem_cma_prime_mmap
gem_prime_mmap is deprecated and on the way out. Only mmap in
drm_gem_object_funcs should be used. I have patches for other drivers
that convert everything to drm_gem_prime_mmap. Afterwards the pointer
can be removed.
Rather than writing a custom prime mmap function, update
drm_gem_cma_prime_import_sg_table() so that it disables non-coherent
mappings for imported buffers. For an example, see how SHMEM's internal
create function uses the 'private' parameter. [1]
Best regards
Thomas
[1]
https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_gem_shmem_helper.c#L39
>
> /**
> * DRM_GEM_CMA_DRIVER_OPS - CMA GEM driver operations
> @@ -181,5 +184,7 @@ struct drm_gem_object *
> drm_gem_cma_prime_import_sg_table_vmap(struct drm_device *drm,
> struct dma_buf_attachment *attach,
> struct sg_table *sgt);
> +int drm_gem_cma_prime_mmap(struct drm_gem_object *obj,
> + struct vm_area_struct *vma);
>
> #endif /* __DRM_GEM_CMA_HELPER_H__ */
>
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer
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