Re: [PATCH 3/9] drm/doc: Some polish for shmem helpers

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, May 11, 2020 at 01:12:49PM +0200, Thomas Zimmermann wrote:
> 
> 
> Am 11.05.20 um 11:35 schrieb Daniel Vetter:
> > - Move the shmem helper section to the drm-mm.rst file, next to the
> >   vram helpers. Makes a lot more sense there with the now wider scope.
> >   Also, that's where the all the other backing storage stuff resides.
> >   It's just the framebuffer helpers that should be in the kms helper
> >   section.
> > 
> > - Try to clarify which functiosn are for implementing
> >   drm_gem_object_funcs, and which for drivers to call directly. At
> >   least one driver screwed that up a bit.
> > 
> > Cc: Gerd Hoffmann <kraxel@redhat.com>
> > Cc: Rob Herring <robh@kernel.org>
> > Cc: Noralf Trønnes <noralf@tronnes.org>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> 
> Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
> 
> See below for a suggestion on the help text.
> 
> > ---
> >  Documentation/gpu/drm-kms-helpers.rst  | 12 --------
> >  Documentation/gpu/drm-mm.rst           | 12 ++++++++
> >  drivers/gpu/drm/drm_gem_shmem_helper.c | 39 +++++++++++++++++++++-----
> >  3 files changed, 44 insertions(+), 19 deletions(-)
> > 
> > diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst
> > index ee730457bf4e..b89ddd06dabb 100644
> > --- a/Documentation/gpu/drm-kms-helpers.rst
> > +++ b/Documentation/gpu/drm-kms-helpers.rst
> > @@ -411,15 +411,3 @@ Legacy CRTC/Modeset Helper Functions Reference
> >  
> >  .. kernel-doc:: drivers/gpu/drm/drm_crtc_helper.c
> >     :export:
> > -
> > -SHMEM GEM Helper Reference
> > -==========================
> > -
> > -.. kernel-doc:: drivers/gpu/drm/drm_gem_shmem_helper.c
> > -   :doc: overview
> > -
> > -.. kernel-doc:: include/drm/drm_gem_shmem_helper.h
> > -   :internal:
> > -
> > -.. kernel-doc:: drivers/gpu/drm/drm_gem_shmem_helper.c
> > -   :export:
> > diff --git a/Documentation/gpu/drm-mm.rst b/Documentation/gpu/drm-mm.rst
> > index 1839762044be..c01757b0ac25 100644
> > --- a/Documentation/gpu/drm-mm.rst
> > +++ b/Documentation/gpu/drm-mm.rst
> > @@ -373,6 +373,18 @@ GEM CMA Helper Functions Reference
> >  .. kernel-doc:: drivers/gpu/drm/drm_gem_cma_helper.c
> >     :export:
> >  
> > +GEM SHMEM Helper Function Reference
> > +-----------------------------------
> > +
> > +.. kernel-doc:: drivers/gpu/drm/drm_gem_shmem_helper.c
> > +   :doc: overview
> > +
> > +.. kernel-doc:: include/drm/drm_gem_shmem_helper.h
> > +   :internal:
> > +
> > +.. kernel-doc:: drivers/gpu/drm/drm_gem_shmem_helper.c
> > +   :export:
> > +
> >  GEM VRAM Helper Functions Reference
> >  -----------------------------------
> >  
> > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> > index df31e5782eed..2a70159d50ef 100644
> > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> > @@ -103,7 +103,8 @@ EXPORT_SYMBOL_GPL(drm_gem_shmem_create);
> >   * @obj: GEM object to free
> >   *
> >   * This function cleans up the GEM object state and frees the memory used to
> > - * store the object itself.
> > + * store the object itself. It should be used to implement
> > + * &drm_gem_object_funcs.free.
> 
> It should 'only' be used? Or maybe you can say that it should be used by
> drivers that don't implement struct drm_driver.gem_create_object.

Just looked at this, and I'm not clear what you're aiming for. There
doesn't seem to be any misuse for this for other places than the free
hook. And I can't really come up with ideas where that would even work.

What kind of confusion are you trying to clarify with your suggestion?
Maybe I can then reword that into something that also makes sense for me.

Thanks, Daniel

> 
> >   */
> >  void drm_gem_shmem_free_object(struct drm_gem_object *obj)
> >  {
> > @@ -214,7 +215,8 @@ EXPORT_SYMBOL(drm_gem_shmem_put_pages);
> >   * @obj: GEM object
> >   *
> >   * This function makes sure the backing pages are pinned in memory while the
> > - * buffer is exported.
> > + * buffer is exported. It should only be used to implement
> > + * &drm_gem_object_funcs.pin.
> >   *
> >   * Returns:
> >   * 0 on success or a negative error code on failure.
> > @@ -232,7 +234,7 @@ EXPORT_SYMBOL(drm_gem_shmem_pin);
> >   * @obj: GEM object
> >   *
> >   * This function removes the requirement that the backing pages are pinned in
> > - * memory.
> > + * memory. It should only be used to implement &drm_gem_object_funcs.unpin.
> >   */
> >  void drm_gem_shmem_unpin(struct drm_gem_object *obj)
> >  {
> > @@ -285,8 +287,14 @@ static void *drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem)
> >   * drm_gem_shmem_vmap - Create a virtual mapping for a shmem GEM object
> >   * @shmem: shmem GEM object
> >   *
> > - * This function makes sure that a virtual address exists for the buffer backing
> > - * the shmem GEM object.
> > + * This function makes sure that a contiguous kernel virtual address mapping
> > + * exists for the buffer backing the shmem GEM object.
> > + *
> > + * This function can be used to implement &drm_gem_object_funcs.vmap. But it can
> > + * also be called by drivers directly, in which case it will hide the
> > + * differences between dma-buf imported and natively allocated objects.
> > + *
> > + * Acquired mappings should be cleaned up by calling drm_gem_shmem_vunmap().
> >   *
> >   * Returns:
> >   * 0 on success or a negative error code on failure.
> > @@ -330,7 +338,13 @@ static void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem)
> >   * drm_gem_shmem_vunmap - Unmap a virtual mapping fo a shmem GEM object
> >   * @shmem: shmem GEM object
> >   *
> > - * This function removes the virtual address when use count drops to zero.
> > + * This function cleans up a kernel virtual address mapping acquired by
> > + * drm_gem_shmem_vmap(). The mapping is only removed when the use count drops to
> > + * zero.
> > + *
> > + * This function can be used to implement &drm_gem_object_funcs.vmap. But it can
> > + * also be called by drivers directly, in which case it will hide the
> > + * differences between dma-buf imported and natively allocated objects.
> >   */
> >  void drm_gem_shmem_vunmap(struct drm_gem_object *obj, void *vaddr)
> >  {
> > @@ -559,6 +573,8 @@ EXPORT_SYMBOL_GPL(drm_gem_shmem_mmap);
> >   * @p: DRM printer
> >   * @indent: Tab indentation level
> >   * @obj: GEM object
> > + *
> > + * This implements the &drm_gem_object_funcs.info callback.
> >   */
> >  void drm_gem_shmem_print_info(struct drm_printer *p, unsigned int indent,
> >  			      const struct drm_gem_object *obj)
> > @@ -577,7 +593,12 @@ EXPORT_SYMBOL(drm_gem_shmem_print_info);
> >   * @obj: GEM object
> >   *
> >   * This function exports a scatter/gather table suitable for PRIME usage by
> > - * calling the standard DMA mapping API.
> > + * calling the standard DMA mapping API. Drivers should not call this function
> > + * directly, instead it should only be used as an implementation for
> > + * &drm_gem_object_funcs.get_sg_table.
> > + *
> > + * Drivers who need to acquire an scatter/gather table for objects need to call
> > + * drm_gem_shmem_get_pages_sgt() instead.
> >   *
> >   * Returns:
> >   * A pointer to the scatter/gather table of pinned pages or NULL on failure.
> > @@ -599,6 +620,10 @@ EXPORT_SYMBOL_GPL(drm_gem_shmem_get_sg_table);
> >   * the sg table doesn't exist, the pages are pinned, dma-mapped, and a sg
> >   * table created.
> >   *
> > + * This is the main function for drivers to get at backing storage, and it hides
> > + * and difference between dma-buf imported and natively allocated objects.
> > + * drm_gem_shmem_get_sg_table() should not be directly called by drivers.
> > + *
> >   * Returns:
> >   * A pointer to the scatter/gather table of pinned pages or errno on failure.
> >   */
> > 
> 
> -- 
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
> 




-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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