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Message-ID: <fce9aae9-a9f8-1b90-33fc-16cf64888ff7@suse.de>
Date: Sat, 15 May 2021 20:49:08 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Paul Cercueil <paul@...pouillou.net>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>
Cc: Christoph Hellwig <hch@...radead.org>, list@...ndingux.net,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
linux-mips@...r.kernel.org
Subject: Re: [PATCH v4 1/3] drm: Add support for GEM buffers backed by
non-coherent memory
Am 15.05.21 um 16:53 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.
>
> v4: Make sure map_noncoherent is always disabled when creating GEM
> objects meant to be used with dma-buf.
>
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
Acked-by: Thomas Zimmermann <tzimmermann@...e.de>
> ---
> drivers/gpu/drm/drm_gem_cma_helper.c | 38 +++++++++++++++++++++-------
> include/drm/drm_gem_cma_helper.h | 3 +++
> 2 files changed, 32 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c
> index 7942cf05cd93..235c7a63da2b 100644
> --- a/drivers/gpu/drm/drm_gem_cma_helper.c
> +++ b/drivers/gpu/drm/drm_gem_cma_helper.c
> @@ -46,6 +46,7 @@ static const struct drm_gem_object_funcs drm_gem_cma_default_funcs = {
> * __drm_gem_cma_create - Create a GEM CMA object without allocating memory
> * @drm: DRM device
> * @size: size of the object to allocate
> + * @private: true if used for internal purposes
> *
> * This function creates and initializes a GEM CMA object of the given size,
> * but doesn't allocate any memory to back the object.
> @@ -55,11 +56,11 @@ static const struct drm_gem_object_funcs drm_gem_cma_default_funcs = {
> * error code on failure.
> */
> static struct drm_gem_cma_object *
> -__drm_gem_cma_create(struct drm_device *drm, size_t size)
> +__drm_gem_cma_create(struct drm_device *drm, size_t size, bool private)
> {
> struct drm_gem_cma_object *cma_obj;
> struct drm_gem_object *gem_obj;
> - int ret;
> + int ret = 0;
>
> if (drm->driver->gem_create_object)
> gem_obj = drm->driver->gem_create_object(drm, size);
> @@ -73,7 +74,14 @@ __drm_gem_cma_create(struct drm_device *drm, size_t size)
>
> cma_obj = container_of(gem_obj, struct drm_gem_cma_object, base);
>
> - ret = drm_gem_object_init(drm, gem_obj, size);
> + if (private) {
> + drm_gem_private_object_init(drm, gem_obj, size);
> +
> + /* Always use writecombine for dma-buf mappings */
> + cma_obj->map_noncoherent = false;
> + } else {
> + ret = drm_gem_object_init(drm, gem_obj, size);
> + }
> if (ret)
> goto error;
>
> @@ -111,12 +119,19 @@ struct drm_gem_cma_object *drm_gem_cma_create(struct drm_device *drm,
>
> size = round_up(size, PAGE_SIZE);
>
> - cma_obj = __drm_gem_cma_create(drm, size);
> + cma_obj = __drm_gem_cma_create(drm, size, false);
> 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);
> @@ -432,7 +447,7 @@ drm_gem_cma_prime_import_sg_table(struct drm_device
*dev,
> return ERR_PTR(-EINVAL);
>
> /* Create a CMA GEM buffer. */
> - cma_obj = __drm_gem_cma_create(dev, attach->dmabuf->size);
> + cma_obj = __drm_gem_cma_create(dev, attach->dmabuf->size, true);
> if (IS_ERR(cma_obj))
> return ERR_CAST(cma_obj);
>
> @@ -499,8 +514,13 @@ 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);
>
> diff --git a/include/drm/drm_gem_cma_helper.h b/include/drm/drm_gem_cma_helper.h
> index 0a9711caa3e8..cd13508acbc1 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) \
>
--
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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