Re: [PATCH 3/5] drm: Add and export function drm_gem_cma_mmap_noncoherent

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Hi Christoph,

Le mar. 3 nov. 2020 à 19:13, Paul Cercueil <paul@xxxxxxxxxxxxxxx> a écrit :
Hi Christoph,

Le mar. 3 nov. 2020 à 18:50, Christoph Hellwig <hch@xxxxxxxxxxxxx> a écrit :
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@xxxxxxxxxxxxxxx>
 ---
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.

Ok, what would be the correct way to mmap_noncoherent?

Waiting for your input here :)

Cheers,
-Paul


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