[PATCH] drm/gem: add functions to get/put pages

[Rob Clark]

On Thu, Sep 15, 2011 at 5:47 PM, Rob Clark <rob.clark at linaro.org> wrote:
> +/**
> + * drm_gem_get_pages - helper to allocate backing pages for a GEM object
> + * @obj: obj in question
> + * @gfpmask: gfp mask of requested pages
> + */
> +struct page ** drm_gem_get_pages(struct drm_gem_object *obj, gfp_t gfpmask)
> +{


Hmm, in working through tiled buffer support over the weekend, I think
I've hit a case where I want to decouple the physical size (in terms
of pages) from virtual size.. which means I don't want to rely on the
same obj->size value for mmap offset creation as for determining # of
pages to allocate.

Since the patch for drm_gem_{get,put}_pages() doesn't seem to be on
drm-core-next yet, I think the more straightforward thing to do is add
a size (or numpages) arg to the get/put_pages functions resubmit this
patch..

BR,
-R

> +       struct inode *inode;
> +       struct address_space *mapping;
> +       struct page *p, **pages;
> +       int i, npages;
> +
> +       /* This is the shared memory object that backs the GEM resource */
> +       inode = obj->filp->f_path.dentry->d_inode;
> +       mapping = inode->i_mapping;
> +
> +       npages = obj->size >> PAGE_SHIFT;
> +
> +       pages = drm_malloc_ab(npages, sizeof(struct page *));
> +       if (pages == NULL)
> +               return ERR_PTR(-ENOMEM);
> +
> +       gfpmask |= mapping_gfp_mask(mapping);
> +
> +       for (i = 0; i < npages; i++) {
> +               p = shmem_read_mapping_page_gfp(mapping, i, gfpmask);
> +               if (IS_ERR(p))
> +                       goto fail;
> +               pages[i] = p;
> +
> +               /* There is a hypothetical issue w/ drivers that require
> +                * buffer memory in the low 4GB.. if the pages are un-
> +                * pinned, and swapped out, they can end up swapped back
> +                * in above 4GB.  If pages are already in memory, then
> +                * shmem_read_mapping_page_gfp will ignore the gfpmask,
> +                * even if the already in-memory page disobeys the mask.
> +                *
> +                * It is only a theoretical issue today, because none of
> +                * the devices with this limitation can be populated with
> +                * enough memory to trigger the issue.  But this BUG_ON()
> +                * is here as a reminder in case the problem with
> +                * shmem_read_mapping_page_gfp() isn't solved by the time
> +                * it does become a real issue.
> +                *
> +                * See this thread: http://lkml.org/lkml/2011/7/11/238
> +                */
> +               BUG_ON((gfpmask & __GFP_DMA32) &&
> +                               (page_to_pfn(p) >= 0x00100000UL));
> +       }
> +
> +       return pages;
> +
> +fail:
> +       while (i--) {
> +               page_cache_release(pages[i]);
> +       }
> +       drm_free_large(pages);
> +       return ERR_PTR(PTR_ERR(p));
> +}
> +EXPORT_SYMBOL(drm_gem_get_pages);
> +
> +/**
> + * drm_gem_put_pages - helper to free backing pages for a GEM object
> + * @obj: obj in question
> + * @pages: pages to free
> + */
> +void drm_gem_put_pages(struct drm_gem_object *obj, struct page **pages,
> +               bool dirty, bool accessed)
> +{
> +       int i, npages;
> +
> +       npages = obj->size >> PAGE_SHIFT;
> +
> +       for (i = 0; i < npages; i++) {
> +               if (dirty)
> +                       set_page_dirty(pages[i]);
> +
> +               if (accessed)
> +                       mark_page_accessed(pages[i]);
> +
> +               /* Undo the reference we took when populating the table */
> +               page_cache_release(pages[i]);
> +       }
> +
> +       drm_free_large(pages);
> +}
> +EXPORT_SYMBOL(drm_gem_put_pages);
>
>  /**
>  * drm_gem_free_mmap_offset - release a fake mmap offset for an object