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

-Paul


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