[PATCH 2/2 v4] drm/exynos: added userptr feature.

[KOSAKI Motohiro]

> + ? ? ? npages = buf->size >> PAGE_SHIFT;

Why round down? usually we use round up.


> + ? ? ? down_read(&current->mm->mmap_sem);
> +
> + ? ? ? /*
> + ? ? ? ?* Basically, all the pages from get_user_pages() can not be not only
> + ? ? ? ?* migrated by CMA but also swapped out.
> + ? ? ? ?*
> + ? ? ? ?* The migration issue.
> + ? ? ? ?* - Pages reserved by CMA for some device using DMA could be used by
> + ? ? ? ?* kernel and if the device driver wants to use those pages
> + ? ? ? ?* while being used by kernel then the pages are copied into
> + ? ? ? ?* other ones allocated to migrate them and then finally,
> + ? ? ? ?* the device driver can use the pages for itself.
> + ? ? ? ?* Thus, migrated, the pages being accessed by DMA could be changed
> + ? ? ? ?* to other so this situation may incur that DMA accesses any pages
> + ? ? ? ?* it doesn't want.
> + ? ? ? ?*
> + ? ? ? ?* But the use of get_user_pages is safe from such magration issue
> + ? ? ? ?* because all the pages from get_user_pages CAN NOT be not only
> + ? ? ? ?* migrated, but also swapped out.
> + ? ? ? ?*/
> + ? ? ? get_npages = get_user_pages(current, current->mm, userptr,
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? npages, write, 1, buf->pages, NULL);

Why force=1? It is almostly core-dump specific option. Why don't you return
EFAULT when the page has write permission. IOW, Why your Xorg module
don't map memory w/ PROT_WRITE?


> + ? ? ? up_read(&current->mm->mmap_sem);
> + ? ? ? if (get_npages != npages)
> + ? ? ? ? ? ? ? DRM_ERROR("failed to get user_pages.\n");