Hi Imre!
On Sat, Feb 09, 2013 at 05:27:33PM +0200, Imre Deak wrote:
> Add a helper to walk through a scatter list a page at a time. Needed by
> upcoming patches fixing the scatter list walking logic in the i915 driver.
Nice patch, but I think this would make a rather nice addition to the
common scatterlist api in scatterlist.h, maybe called sg_page_iter.
There's already another helper which does cpu mappings, but it has a
different use-case (gives you the page mapped, which we don't neeed and
can cope with not page-aligned sg tables). With dma-buf using sg tables I
expect more users of such a sg page iterator to pop up. Most possible
users of this will hang around on linaro-mm-sig, so please also cc that
besides the usual suspects.
Cheers, Daniel
>
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
> include/drm/drmP.h | 44 ++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 44 insertions(+)
>
> diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> index fad21c9..0c0c213 100644
> --- a/include/drm/drmP.h
> +++ b/include/drm/drmP.h
> @@ -1578,6 +1578,50 @@ extern int drm_sg_alloc_ioctl(struct drm_device *dev, void *data,
> extern int drm_sg_alloc(struct drm_device *dev, struct drm_scatter_gather * request);
> extern int drm_sg_free(struct drm_device *dev, void *data,
> struct drm_file *file_priv);
> +struct drm_sg_iter {
> + struct scatterlist *sg;
> + int sg_offset;
Imo using sg_pfn_offset (i.e. sg_offset >> PAGE_SIZE) would make it
clearer that this is all about iterating page-aligned sg tables.
> + struct page *page;
> +};
> +
> +static inline int
> +__drm_sg_iter_seek(struct drm_sg_iter *iter)
> +{
> + while (iter->sg && iter->sg_offset >= iter->sg->length) {
> + iter->sg_offset -= iter->sg->length;
> + iter->sg = sg_next(iter->sg);
And adding a WARN_ON(sg->legnth & ~PAGE_MASK); here would enforce that.
> + }
> +
> + return iter->sg ? 0 : -1;
> +}
> +
> +static inline struct page *
> +drm_sg_iter_next(struct drm_sg_iter *iter)
> +{
> + struct page *page;
> +
> + if (__drm_sg_iter_seek(iter))
> + return NULL;
> +
> + page = nth_page(sg_page(iter->sg), iter->sg_offset >> PAGE_SHIFT);
> + iter->sg_offset = (iter->sg_offset + PAGE_SIZE) & PAGE_MASK;
> +
> + return page;
> +}
> +
> +static inline struct page *
> +drm_sg_iter_start(struct drm_sg_iter *iter, struct scatterlist *sg,
> + unsigned long offset)
> +{
> + iter->sg = sg;
> + iter->sg_offset = offset;
> +
> + return drm_sg_iter_next(iter);
> +}
> +
> +#define drm_for_each_sg_page(iter, sg, pgoffset) \
> + for ((iter)->page = drm_sg_iter_start((iter), (sg), (pgoffset));\
> + (iter)->page; (iter)->page = drm_sg_iter_next(iter))
Again, for the initialization I'd go with page numbers, not an offset in
bytes.
>
> /* ATI PCIGART support (ati_pcigart.h) */
> extern int drm_ati_pcigart_init(struct drm_device *dev,
> --
> 1.7.10.4
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
