Re: [PATCH v2 3/5] drm: Add and export function drm_gem_cma_mmap_noncoherent

Paul Cercueil
2021-03-11T12:33:46Z

Hi Christoph,

Le jeu. 11 mars 2021 à 12:26, Christoph Hellwig <hch@infradead.org> a
écrit :
>> +int drm_gem_cma_mmap_noncoherent(struct drm_gem_object *obj,
>> + struct vm_area_struct *vma)
>> +{
>> + struct drm_gem_cma_object *cma_obj;
>> + unsigned long pfn;
>> + int ret;
>> +
>> + /*
>> + * 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_pgoff -= drm_vma_node_start(&obj->vma_node);
>> + vma->vm_flags &= ~VM_PFNMAP;
>> + vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
>> +
>> + cma_obj = to_drm_gem_cma_obj(obj);
>> +
>> + pfn = PHYS_PFN(dma_to_phys(cma_obj->base.dev->dev,
>> cma_obj->paddr));
>> +
>> + ret = remap_pfn_range(vma, vma->vm_start, pfn,
>> + vma->vm_end - vma->vm_start,
>> + vma->vm_page_prot);
>
> dma_to_phys must not be used by drivers.
>
> I have a proper helper for this waiting for users:
>
> http://git.infradead.org/users/hch/misc.git/commitdiff/96a546e7229ec53aadbdb7936d1e5e6cb5958952
>
> If you can confirm the helpers works for you I can try to still sneak
> it to Linus for 5.12 to ease the merge pain.

I can try. How do I get a page pointer from a dma_addr_t?

-Paul