Re: [PATCH 1/2] drm/panfrost: Allow passing extra information about BOs used by a job

[Rob Herring <robh+dt@kernel.org>]

On Fri, Sep 13, 2019 at 8:44 AM Steven Price <steven.price@arm.com> wrote:
>
> On 13/09/2019 12:17, Boris Brezillon wrote:
> > The READ/WRITE flags are particularly useful if we want to avoid
> > serialization of jobs that read from the same BO but never write to it.
> > The NO_IMPLICIT_FENCE might be useful when the user knows the BO is
> > shared but jobs are using different portions of the buffer.
> >
> > Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
>
> Good feature - we could do with an (easy) way of the user driver
> detecting this - so it might be worth bumping the driver version for this?
>
> Some more comments below.
>
> > ---
> >  drivers/gpu/drm/panfrost/panfrost_drv.c |  72 +++++++++--
> >  drivers/gpu/drm/panfrost/panfrost_job.c | 164 +++++++++++++++++++-----
> >  drivers/gpu/drm/panfrost/panfrost_job.h |  11 +-
> >  include/uapi/drm/panfrost_drm.h         |  41 ++++++
> >  4 files changed, 247 insertions(+), 41 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> > index d74442d71048..08082fd557c3 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> > @@ -119,20 +119,76 @@ panfrost_lookup_bos(struct drm_device *dev,
> >                 struct drm_panfrost_submit *args,
> >                 struct panfrost_job *job)
> >  {
> > -     job->bo_count = args->bo_handle_count;
> > +     struct drm_panfrost_submit_bo *bo_descs = NULL;
> > +     u32 *handles = NULL;
> > +     u32 i, bo_count;
> > +     int ret = 0;
> >
> > -     if (!job->bo_count)
> > +     bo_count = args->bo_desc_count ?
> > +                args->bo_desc_count : args->bo_handle_count;
> > +     if (!bo_count)
> >               return 0;
> >
> > -     job->implicit_fences = kvmalloc_array(job->bo_count,
> > -                               sizeof(struct dma_fence *),
> > +     job->bos = kvmalloc_array(bo_count, sizeof(*job->bos),
> >                                 GFP_KERNEL | __GFP_ZERO);
> > -     if (!job->implicit_fences)
> > +     if (!job->bos)
> >               return -ENOMEM;
> >
> > -     return drm_gem_objects_lookup(file_priv,
> > -                                   (void __user *)(uintptr_t)args->bo_handles,
> > -                                   job->bo_count, &job->bos);
> > +     job->bo_count = bo_count;
> > +     bo_descs = kvmalloc_array(bo_count, sizeof(*bo_descs),
> > +                               GFP_KERNEL | __GFP_ZERO);
> > +     if (!bo_descs) {
> > +             ret = -ENOMEM;
> > +             goto out;
>
> This can be just "return -ENOMEM" - both handles and bo_descs will be NULL.
>
> > +     }
> > +
> > +     if (!args->bo_desc_count) {
> > +             handles = kvmalloc_array(bo_count, sizeof(*handles),
> > +                                      GFP_KERNEL);
> > +             if (!handles) {
> > +                     ret =-ENOMEM;
> > +                     goto out;
> > +             }
> > +
> > +             if (copy_from_user(handles,
> > +                                (void __user *)(uintptr_t)args->bo_handles,
> > +                                job->bo_count * sizeof(*handles))) {
> > +                     ret = -EFAULT;
> > +                     goto out;
> > +             }
> > +
> > +             for (i = 0; i < job->bo_count; i++) {
> > +                     bo_descs[i].handle = handles[i];
> > +                     bo_descs[i].flags = PANFROST_SUBMIT_BO_WRITE |
> > +                                         PANFROST_SUBMIT_BO_READ;
>
> You can use PANFROST_SUBMIT_BO_RW here.
>
> > +             }
> > +     } else if (copy_from_user(bo_descs,
> > +                               (void __user *)(uintptr_t)args->bo_descs,
> > +                               job->bo_count * sizeof(*bo_descs))) {
> > +             ret = -EFAULT;
> > +             goto out;
> > +     }
> > +
> > +     for (i = 0; i < job->bo_count; i++) {
> > +             if ((bo_descs[i].flags & ~PANFROST_SUBMIT_BO_VALID_FLAGS) ||
> > +                    !(bo_descs[i].flags & PANFROST_SUBMIT_BO_RW)) {
> > +                     ret = -EINVAL;
> > +                     goto out;
> > +             }
> > +
> > +             job->bos[i].flags = bo_descs[i].flags;
> > +             job->bos[i].obj = drm_gem_object_lookup(file_priv,
> > +                                                     bo_descs[i].handle);
> > +             if (!job->bos[i].obj) {
> > +                     ret = -ENOENT;
> > +                     goto out;
> > +             }
> > +     }
> > +
> > +out:
> > +     kvfree(handles);
> > +     kvfree(bo_descs);
> > +     return ret;
> >  }
> >
> >  /**
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
> > index 05c85f45a0de..e4b74fde9339 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> > @@ -193,24 +193,116 @@ static void panfrost_job_hw_submit(struct panfrost_job *job, int js)
> >       pm_runtime_put_autosuspend(pfdev->dev);
> >  }
> >
> > -static void panfrost_acquire_object_fences(struct drm_gem_object **bos,
> > -                                        int bo_count,
> > -                                        struct dma_fence **implicit_fences)
> > +static int panfrost_acquire_object_fences(struct panfrost_job *job)
> >  {
> > -     int i;
> > +     int i, ret;
> >
> > -     for (i = 0; i < bo_count; i++)
> > -             implicit_fences[i] = dma_resv_get_excl_rcu(bos[i]->resv);
> > +     for (i = 0; i < job->bo_count; i++) {
> > +             struct panfrost_job_bo_desc *bo = &job->bos[i];
> > +             struct dma_resv *robj = bo->obj->resv;
> > +
> > +             if (!(job->bos[i].flags & PANFROST_SUBMIT_BO_WRITE)) {
> > +                     ret = dma_resv_reserve_shared(robj, 1);
> > +                     if (ret)
> > +                             return ret;
> > +             }
> > +
> > +             if (bo->flags & PANFROST_SUBMIT_BO_NO_IMPLICIT_FENCE)
> > +                     continue;
> > +
> > +             if (bo->flags & PANFROST_SUBMIT_BO_WRITE) {
> > +                     ret = dma_resv_get_fences_rcu(robj, &bo->excl,
> > +                                                   &bo->shared_count,
> > +                                                   &bo->shared);
> > +                     if (ret)
> > +                             return ret;
> > +             } else {
> > +                     bo->excl = dma_resv_get_excl_rcu(robj);
> > +             }
>
> The implementation of NO_IMPLICIT_FENCE seems a bit strange to me: READ
> | NO_IMPLICIT_FENCE still reserves space for a shared fence. I don't
> understand why.
>
> > +     }
> > +
> > +     return 0;
> >  }
> >
> > -static void panfrost_attach_object_fences(struct drm_gem_object **bos,
> > -                                       int bo_count,
> > -                                       struct dma_fence *fence)
> > +static void panfrost_attach_object_fences(struct panfrost_job *job)
> >  {
> >       int i;
> >
> > -     for (i = 0; i < bo_count; i++)
> > -             dma_resv_add_excl_fence(bos[i]->resv, fence);
> > +     for (i = 0; i < job->bo_count; i++) {
> > +             struct drm_gem_object *obj = job->bos[i].obj;
> > +
> > +             if (job->bos[i].flags & PANFROST_SUBMIT_BO_WRITE)
> > +                     dma_resv_add_excl_fence(obj->resv,
> > +                                             job->render_done_fence);
> > +             else
> > +                     dma_resv_add_shared_fence(obj->resv,
> > +                                               job->render_done_fence);
> > +     }
> > +}
> > +
> > +static int panfrost_job_lock_bos(struct panfrost_job *job,
> > +                              struct ww_acquire_ctx *acquire_ctx)
> > +{
> > +     int contended = -1;
> > +     int i, ret;
> > +
> > +     ww_acquire_init(acquire_ctx, &reservation_ww_class);
> > +
> > +retry:
> > +     if (contended != -1) {
> > +             struct drm_gem_object *obj = job->bos[contended].obj;
> > +
> > +             ret = ww_mutex_lock_slow_interruptible(&obj->resv->lock,
> > +                                                    acquire_ctx);
>
> dma_resv_lock_slot_interruptible()?
>
> > +             if (ret) {
> > +                     ww_acquire_done(acquire_ctx);
> > +                     return ret;
> > +             }
> > +     }
> > +
> > +     for (i = 0; i < job->bo_count; i++) {
> > +             if (i == contended)
> > +                     continue;
> > +
> > +             ret = ww_mutex_lock_interruptible(&job->bos[i].obj->resv->lock,
> > +                                               acquire_ctx);
>
> dma_resv_lock_interruptible()?
>
> > +             if (ret) {
> > +                     int j;
> > +
> > +                     for (j = 0; j < i; j++)
> > +                             ww_mutex_unlock(&job->bos[j].obj->resv->lock);
> > +
> > +                     if (contended != -1 && contended >= i) {
> > +                             struct drm_gem_object *contended_obj;
> > +
> > +                             contended_obj = job->bos[contended].obj;
> > +                             ww_mutex_unlock(&contended_obj->resv->lock);
> > +                     }
> > +
> > +                     if (ret == -EDEADLK) {
> > +                             contended = i;
> > +                             goto retry;
> > +                     }
> > +
> > +                     ww_acquire_done(acquire_ctx);
> > +                     return ret;
> > +             }
> > +     }
> > +
> > +     ww_acquire_done(acquire_ctx);
> > +
> > +     return 0;
> > +}
>
> This looks like a copy of drm_gem_lock_reservations(). The only reason
> for it as far as I can see is because we now have an array of struct
> panfrost_job_bo_desc rather than a direct array of struct
> drm_gem_object. I'm not sure having everything neatly in one structure
> is worth this cost?

I'm not thrilled about this either. If not a separate array, we could
change the common code to work on a common struct instead.

To put it another way, this is all copy-n-paste from elsewhere that I
don't really understand and want to maintain in the driver.

Rob
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