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

Hi Christoph,

Le mar. 3 nov. 2020 à 19:13, Paul Cercueil paul@crapouillou.net a écrit :

Hi Christoph,

Le mar. 3 nov. 2020 à 18:50, Christoph Hellwig hch@infradead.org 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@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.

Ok, what would be the correct way to mmap_noncoherent?

Waiting for your input here :)

Cheers, -Paul