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SubjectRe: [PATCH 3/5] drm: Add and export function drm_gem_cma_mmap_noncoherent
On Mon, Nov 02, 2020 at 10:06:49PM +0000, Paul Cercueil wrote:
> This function can be used by drivers that need to mmap dumb buffers
> created with non-coherent backing memory.
>
> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> ---
> drivers/gpu/drm/drm_gem_cma_helper.c | 39 ++++++++++++++++++++++++++++
> include/drm/drm_gem_cma_helper.h | 2 ++
> 2 files changed, 41 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c
> index 3bdd67795e20..4ed63f4896bd 100644
> --- a/drivers/gpu/drm/drm_gem_cma_helper.c
> +++ b/drivers/gpu/drm/drm_gem_cma_helper.c
> @@ -387,6 +387,45 @@ int drm_gem_cma_mmap(struct file *filp, struct vm_area_struct *vma)
> }
> EXPORT_SYMBOL_GPL(drm_gem_cma_mmap);
>
> +/**
> + * drm_gem_cma_mmap_noncoherent - memory-map a CMA GEM object with
> + * non-coherent cache attribute
> + * @filp: file object
> + * @vma: VMA for the area to be mapped
> + *
> + * Just like drm_gem_cma_mmap, but for a GEM object backed by non-coherent
> + * memory.
> + *
> + * Returns:
> + * 0 on success or a negative error code on failure.
> + */
> +int drm_gem_cma_mmap_noncoherent(struct file *filp, struct vm_area_struct *vma)
> +{
> + struct drm_gem_cma_object *cma_obj;
> + int ret;
> +
> + ret = drm_gem_mmap(filp, vma);
> + if (ret)
> + return ret;
> +
> + cma_obj = to_drm_gem_cma_obj(vma->vm_private_data);
> +
> + /*
> + * Clear the VM_PFNMAP flag that was set by drm_gem_mmap(), and set the
> + * vm_pgoff (used as a fake buffer offset by DRM) to 0 as we want to map
> + * the whole buffer.
> + */
> + vma->vm_flags &= ~VM_PFNMAP;
> + vma->vm_pgoff = 0;
> + vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
> +
> + return remap_pfn_range(vma, vma->vm_start,
> + cma_obj->paddr >> PAGE_SHIFT,
> + vma->vm_end - vma->vm_start,
> + vma->vm_page_prot);

Per patch 1 cma_obj->paddr is the dma address, while remap_pfn_range
expects a physical address. This does not work.

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