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Message-ID: <26b5424a-ff4c-090b-a08f-0e3e32278180@ideasonboard.com>
Date: Thu, 27 May 2021 13:40:07 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Paul Cercueil <paul@...pouillou.net>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>
Cc: linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
linux-mips@...r.kernel.org, Christoph Hellwig <hch@...radead.org>,
list@...ndingux.net, Lokesh Vutla <lokeshvutla@...com>,
"Yadav, Pratyush" <p.yadav@...com>
Subject: Re: [PATCH v5 1/3] drm: Add support for GEM buffers backed by
non-coherent memory
On 23/05/2021 20:04, Paul Cercueil wrote:
> 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));
This breaks mmap on TI's J7 EVM (tidss driver). All DRM apps just die
when doing mmap. Changing these lines back to dma_mmap_wc() makes it work.
Is dma_alloc_wc() even compatible with dma_mmap_pages()?
Tomi
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