Re: [PATCH 1/4] drm: add prime helpers

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Dec 06, 2012 at 10:46:30PM +0100, Daniel Vetter wrote:
> On Thu, Dec 06, 2012 at 10:07:48AM -0800, Aaron Plattner wrote:
> > Instead of reimplementing all of the dma_buf functionality in every driver,
> > create helpers drm_prime_import and drm_prime_export that implement them in
> > terms of new, lower-level hook functions:
> > 
> >   gem_prime_pin: callback when a buffer is created, used to pin buffers into GTT
> >   gem_prime_get_pages: convert a drm_gem_object to an sg_table for export
> >   gem_prime_import_sg: convert an sg_table into a drm_gem_object
> >   gem_prime_vmap, gem_prime_vunmap: map and unmap an object
> > 
> > These hooks are optional; drivers can opt in by using drm_gem_prime_import and
> > drm_gem_prime_export as the .gem_prime_import and .gem_prime_export fields of
> > struct drm_driver.
> > 
> > Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
> 
> A few comments:
> 
> - Can you please add kerneldoc entries for these new helpers? Laurent
>   Pinchart started a nice drm kerneldoc as an overview. And since then
>   we've at least integrated the kerneldoc api reference at a nice place
>   there and brushed it up a bit when touching drm core or helpers in a
>   bigger patch series. See e.g. my recent dp helper series for what I'm
>   looking for. I think we should have kerneldoc at least for the exported
>   functions.
> 
> - Just an idea for all the essential noop cpu helpers: Maybe just call
>   them dma_buf*noop and shovel them as convenience helpers into the
>   dma-buf.c code in the core, for drivers that don't want/can't/won't
>   bother to implement the cpu access support. Related: Exporting the
>   functions in general so that drivers could pick&choose

One more: For the cpu access noop helpers I'd vote for -ENOTTY as the more
canonical "not implemented error, you're talking to the wrong thing" error
instead of -EINVAL, which an exporter could throw back to the importer if
e.g. the range is outside of the size of the dma_buf. With a quick dma_buf
doc update we could then bless this as the official way to denounce cpu
access support.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch