Re: [PATCH v18 04/26] drm/shmem-helper: Refactor locked/unlocked functions

[Boris Brezillon]

On Fri, 24 Nov 2023 11:40:06 +0100
Maxime Ripard <mripard@xxxxxxxxxx> wrote:

> On Mon, Oct 30, 2023 at 02:01:43AM +0300, Dmitry Osipenko wrote:
> > Add locked and remove unlocked postfixes from drm-shmem function names,
> > making names consistent with the drm/gem core code.
> > 
> > Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> > Suggested-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> > Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>  
> 
> This contradicts my earlier ack on a patch but...
> 
> > ---
> >  drivers/gpu/drm/drm_gem_shmem_helper.c        | 64 +++++++++----------
> >  drivers/gpu/drm/lima/lima_gem.c               |  8 +--
> >  drivers/gpu/drm/panfrost/panfrost_drv.c       |  2 +-
> >  drivers/gpu/drm/panfrost/panfrost_gem.c       |  6 +-
> >  .../gpu/drm/panfrost/panfrost_gem_shrinker.c  |  2 +-
> >  drivers/gpu/drm/panfrost/panfrost_mmu.c       |  2 +-
> >  drivers/gpu/drm/v3d/v3d_bo.c                  |  4 +-
> >  drivers/gpu/drm/virtio/virtgpu_object.c       |  4 +-
> >  include/drm/drm_gem_shmem_helper.h            | 36 +++++------
> >  9 files changed, 64 insertions(+), 64 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> > index 0d61f2b3e213..154585ddae08 100644
> > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> > @@ -43,8 +43,8 @@ static const struct drm_gem_object_funcs drm_gem_shmem_funcs = {
> >  	.pin = drm_gem_shmem_object_pin,
> >  	.unpin = drm_gem_shmem_object_unpin,
> >  	.get_sg_table = drm_gem_shmem_object_get_sg_table,
> > -	.vmap = drm_gem_shmem_object_vmap,
> > -	.vunmap = drm_gem_shmem_object_vunmap,
> > +	.vmap = drm_gem_shmem_object_vmap_locked,
> > +	.vunmap = drm_gem_shmem_object_vunmap_locked,  
> 
> While I think we should indeed be consistent with the names, I would
> also expect helpers to get the locking right by default.

Wait, actually I think this patch does what you suggest already. The
_locked() prefix tells the caller: "you should take care of the locking,
I expect the lock to be held when this is hook/function is called". So
helpers without the _locked() prefix take care of the locking (which I
guess matches your 'helpers get the locking right' expectation), and
those with the _locked() prefix don't.

> 
> I'm not sure how reasonable it is, but I think I'd prefer to turn this
> around and keep the drm_gem_shmem_object_vmap/unmap helpers name, and
> convert whatever function needs to be converted to the unlock suffix so
> we get a consistent naming.

That would be an _unlocked() prefix if we do it the other way around. I
think the main confusion comes from the names of the hooks in
drm_gem_shmem_funcs. Some of them, like drm_gem_shmem_funcs::v[un]map()
are called with the GEM resv lock held, and locking is handled by the
core, others, like drm_gem_shmem_funcs::[un]pin() are called
without the GEM resv lock held, and locking is deferred to the
implementation. As I said, I don't mind prefixing hooks/helpers with
_unlocked() for those that take care of the locking, and no prefix for
those that expects locks to be held, as long as it's consistent, but I
just wanted to make sure we're on the same page :-).