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

[Rob Clark]

On Mon, Sep 26, 2011 at 2:43 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Mon, Sep 26, 2011 at 01:18:40PM -0500, Rob Clark wrote:
>> 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..
>
> I think making obj->size not be the size of the backing storage is the
> wrong thing. In i915 we have a similar issue with tiled regions on gen2/3:
> The minimal sizes for these are pretty large, so objects are smaller than
> a the tiled region. So backing storage and maps are both obj->size large,
> but the area the object occupies in the gtt may be much large. To put some
> packing storage behind the not-used region (which sounds like what you're
> trying to do here) we simply use one global dummy page. Userspace should
> never use this, so that's fine.
>
> Or is this a case of insane arm hw, and you can't actually put the same
> physical page at different gtt locations?

Well, the "GART" in our case is a bit restrictive.. we can have same
page in multiple locations, but not arbitrary locations.  Things need
to go to slot boundaries.  So it isn't really possible to get row n+1
to appear directly after row n.  To handle this we just round the
buffer stride up to next 4kb boundary and insert some dummy page the
the remaining slots to pad out to 4kb.

The only other way I could think of to handle that would be to have a
separate vsize and psize in 'struct drm_gem_object'..

BR,
-R


>
> -Daniel
> --
> Daniel Vetter
> Mail: daniel at ffwll.ch
> Mobile: +41 (0)79 365 57 48
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