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From:   Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Date:   Tue, 21 Nov 2023 15:14:28 +0200
Message-ID: <CAA8EJprj7F_K1zxnGdz1ReLNMR2CiYfRxWHUmudTZC+qjKA+kA@mail.gmail.com>
Subject: Re: [PATCH v2] Remove custom dumb_map_offset implementation in msm driver
To:     Rob Clark <robdclark@gmail.com>
Cc:     Dipam Turkar <dipamt1729@gmail.com>, quic_abhinavk@quicinc.com,
        sean@poorly.run, marijn.suijten@somainline.org, airlied@gmail.com,
        daniel@ffwll.ch, linux-arm-msm@vger.kernel.org,
        dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
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On Tue, 21 Nov 2023 at 04:26, Rob Clark <robdclark@gmail.com> wrote:
>
> On Wed, Nov 15, 2023 at 11:33=E2=80=AFAM Dmitry Baryshkov
> <dmitry.baryshkov@linaro.org> wrote:
> >
> > On Wed, 15 Nov 2023 at 20:46, Dipam Turkar <dipamt1729@gmail.com> wrote=
:
> > >
> > > They are not outdated, my bad. I went through the locks' code and saw=
 that they have been updated. But they are probably not necessary here as m=
ost of the drivers do not use any form of locking in their implementations.=
 The generic implementations drm_gem_dumb_map_offset() and drm_gem_ttm_dumb=
_map_offset() do not have any locking mechanisms either.
> >
> > Excuse me, but this doesn't sound right to me. There are different
> > drivers with different implementations. So either we'd need a good
> > explanation of why it is not necessary, or this patch is NAKed.
>
> Digging a bit thru history, it looks like commit 0de23977cfeb
> ("drm/gem: convert to new unified vma manager") made external locking
> unnecessary, since the vma mgr already had it's own internal locking.

So, should we drop our own locking system?

>
> BR,
> -R
>
> > >
> > > Thanks and regards
> > > Dipam Turkar
> > >
> > > On Wed, Nov 15, 2023 at 8:37=E2=80=AFPM Dmitry Baryshkov <dmitry.bary=
shkov@linaro.org> wrote:
> > >>
> > >> On Wed, 15 Nov 2023 at 16:30, Dipam Turkar <dipamt1729@gmail.com> wr=
ote:
> > >> >
> > >> > Make msm use drm_gem_create_map_offset() instead of its custom
> > >> > implementation for associating GEM object with a fake offset. Sinc=
e,
> > >> > we already have this generic implementation, we don't need the cus=
tom
> > >> > implementation and it is better to standardize the code for GEM ba=
sed
> > >> > drivers. This also removes the outdated locking leftovers.
> > >>
> > >> Why are they outdated?
> > >>
> > >> >
> > >> > Signed-off-by: Dipam Turkar <dipamt1729@gmail.com>
> > >> > ---
> > >> >  drivers/gpu/drm/msm/msm_drv.c |  2 +-
> > >> >  drivers/gpu/drm/msm/msm_gem.c | 21 ---------------------
> > >> >  drivers/gpu/drm/msm/msm_gem.h |  2 --
> > >> >  3 files changed, 1 insertion(+), 24 deletions(-)
> > >> >
> > >> > Changes in v2:
> > >> > Modify commit message to include the absence of internal locking l=
eftovers
> > >> > around allocating a fake offset in msm_gem_mmap_offset() in the ge=
neric
> > >> > implementation drm_gem_create_map_offset().
> > >> >
> > >> > diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/m=
sm_drv.c
> > >> > index a428951ee539..86a15992c717 100644
> > >> > --- a/drivers/gpu/drm/msm/msm_drv.c
> > >> > +++ b/drivers/gpu/drm/msm/msm_drv.c
> > >> > @@ -1085,7 +1085,7 @@ static const struct drm_driver msm_driver =
=3D {
> > >> >         .open               =3D msm_open,
> > >> >         .postclose          =3D msm_postclose,
> > >> >         .dumb_create        =3D msm_gem_dumb_create,
> > >> > -       .dumb_map_offset    =3D msm_gem_dumb_map_offset,
> > >> > +       .dumb_map_offset    =3D drm_gem_dumb_map_offset,
> > >> >         .gem_prime_import_sg_table =3D msm_gem_prime_import_sg_tab=
le,
> > >> >  #ifdef CONFIG_DEBUG_FS
> > >> >         .debugfs_init       =3D msm_debugfs_init,
> > >> > diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/m=
sm_gem.c
> > >> > index db1e748daa75..489694ef79cb 100644
> > >> > --- a/drivers/gpu/drm/msm/msm_gem.c
> > >> > +++ b/drivers/gpu/drm/msm/msm_gem.c
> > >> > @@ -671,27 +671,6 @@ int msm_gem_dumb_create(struct drm_file *file=
, struct drm_device *dev,
> > >> >                         MSM_BO_SCANOUT | MSM_BO_WC, &args->handle,=
 "dumb");
> > >> >  }
> > >> >
> > >> > -int msm_gem_dumb_map_offset(struct drm_file *file, struct drm_dev=
ice *dev,
> > >> > -               uint32_t handle, uint64_t *offset)
> > >> > -{
> > >> > -       struct drm_gem_object *obj;
> > >> > -       int ret =3D 0;
> > >> > -
> > >> > -       /* GEM does all our handle to object mapping */
> > >> > -       obj =3D drm_gem_object_lookup(file, handle);
> > >> > -       if (obj =3D=3D NULL) {
> > >> > -               ret =3D -ENOENT;
> > >> > -               goto fail;
> > >> > -       }
> > >> > -
> > >> > -       *offset =3D msm_gem_mmap_offset(obj);
> > >> > -
> > >> > -       drm_gem_object_put(obj);
> > >> > -
> > >> > -fail:
> > >> > -       return ret;
> > >> > -}
> > >> > -
> > >> >  static void *get_vaddr(struct drm_gem_object *obj, unsigned madv)
> > >> >  {
> > >> >         struct msm_gem_object *msm_obj =3D to_msm_bo(obj);
> > >> > diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/m=
sm_gem.h
> > >> > index 8ddef5443140..dc74a0ef865d 100644
> > >> > --- a/drivers/gpu/drm/msm/msm_gem.h
> > >> > +++ b/drivers/gpu/drm/msm/msm_gem.h
> > >> > @@ -139,8 +139,6 @@ struct page **msm_gem_pin_pages(struct drm_gem=
_object *obj);
> > >> >  void msm_gem_unpin_pages(struct drm_gem_object *obj);
> > >> >  int msm_gem_dumb_create(struct drm_file *file, struct drm_device =
*dev,
> > >> >                 struct drm_mode_create_dumb *args);
> > >> > -int msm_gem_dumb_map_offset(struct drm_file *file, struct drm_dev=
ice *dev,
> > >> > -               uint32_t handle, uint64_t *offset);
> > >> >  void *msm_gem_get_vaddr_locked(struct drm_gem_object *obj);
> > >> >  void *msm_gem_get_vaddr(struct drm_gem_object *obj);
> > >> >  void *msm_gem_get_vaddr_active(struct drm_gem_object *obj);
> > >> > --
> > >> > 2.34.1
> > >> >
> > >>
> > >>
> > >> --
> > >> With best wishes
> > >> Dmitry
> >
> >
> >
> > --
> > With best wishes
> > Dmitry


--=20
With best wishes
Dmitry