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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 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


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