Re: [PATCH 2/2] drm/msm/dpu: clean up some impossibilities

[Rob Clark]

On Tue, Sep 8, 2020 at 12:44 PM <abhinavk@xxxxxxxxxxxxxx> wrote:
>
> On 2020-09-07 10:04, Rob Clark wrote:
> > From: Rob Clark <robdclark@xxxxxxxxxxxx>
> >
> > Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
> > ---
> >  drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c | 81 ++++--------------------
> >  1 file changed, 12 insertions(+), 69 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> > b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> > index 89c0245b5de5..ad49b0e17fcb 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> > @@ -265,11 +265,6 @@ enum dpu_intf_mode dpu_crtc_get_intf_mode(struct
> > drm_crtc *crtc)
> >  {
> >       struct drm_encoder *encoder;
> >
> > -     if (!crtc) {
> > -             DPU_ERROR("invalid crtc\n");
> > -             return INTF_MODE_NONE;
> > -     }
> > -
> >       /*
> >        * TODO: This function is called from dpu debugfs and as part of
> > atomic
> >        * check. When called from debugfs, the crtc->mutex must be held to
> > @@ -500,12 +495,6 @@ static void dpu_crtc_atomic_begin(struct drm_crtc
> > *crtc,
> >       struct dpu_crtc_state *cstate;
> >       struct drm_encoder *encoder;
> >       struct drm_device *dev;
> > -     unsigned long flags;
> > -
> > -     if (!crtc) {
> > -             DPU_ERROR("invalid crtc\n");
> > -             return;
> > -     }
> >
> >       if (!crtc->state->enable) {
> >               DPU_DEBUG("crtc%d -> enable %d, skip atomic_begin\n",
> > @@ -521,15 +510,6 @@ static void dpu_crtc_atomic_begin(struct drm_crtc
> > *crtc,
> >
> >       _dpu_crtc_setup_lm_bounds(crtc, crtc->state);
> >
> > -     if (dpu_crtc->event) {
> > -             WARN_ON(dpu_crtc->event);
> > -     } else {
> > -             spin_lock_irqsave(&dev->event_lock, flags);
> > -             dpu_crtc->event = crtc->state->event;
> > -             crtc->state->event = NULL;
> > -             spin_unlock_irqrestore(&dev->event_lock, flags);
> > -     }
> > -
> >       /* encoder will trigger pending mask now */
> >       drm_for_each_encoder_mask(encoder, crtc->dev,
> > crtc->state->encoder_mask)
> >               dpu_encoder_trigger_kickoff_pending(encoder);
> > @@ -583,14 +563,11 @@ static void dpu_crtc_atomic_flush(struct drm_crtc
> > *crtc,
> >               return;
> >       }
> >
> > -     if (dpu_crtc->event) {
> > -             DPU_DEBUG("already received dpu_crtc->event\n");
> > -     } else {
> > -             spin_lock_irqsave(&dev->event_lock, flags);
> > -             dpu_crtc->event = crtc->state->event;
> > -             crtc->state->event = NULL;
> > -             spin_unlock_irqrestore(&dev->event_lock, flags);
> > -     }
> > +     WARN_ON(dpu_crtc->event);
> before the patch "move vblank events to complete_commit()", the dpu_crtc
> events
> were consumed in the _dpu_crtc_complete_flip(). So there was a chance
> that if the vblank event
> did not come in time before the next commit, dpu_crtc->event will not be
> consumed.
>
> But after the patch, _dpu_crtc_complete_flip() is being signaled in
> dpu_crtc_complete_commit()
> which will always happen, so is there any case where we will hit this
> warning at all or will this
> catch some other condition?

The core drm-atomic bits will reject an incoming atomic update if the
previous one has not completed, so other than a coding bug, this
WARN_ON() should not be hit..  it's only purpose is to make it very
obvious if someone breaks something :-)

BR,
-R

>
> > +     spin_lock_irqsave(&dev->event_lock, flags);
> > +     dpu_crtc->event = crtc->state->event;
> > +     crtc->state->event = NULL;
> > +     spin_unlock_irqrestore(&dev->event_lock, flags);
> >
> >       /*
> >        * If no mixers has been allocated in dpu_crtc_atomic_check(),
> > @@ -635,14 +612,7 @@ static void dpu_crtc_atomic_flush(struct drm_crtc
> > *crtc,
> >  static void dpu_crtc_destroy_state(struct drm_crtc *crtc,
> >               struct drm_crtc_state *state)
> >  {
> > -     struct dpu_crtc_state *cstate;
> > -
> > -     if (!crtc || !state) {
> > -             DPU_ERROR("invalid argument(s)\n");
> > -             return;
> > -     }
> > -
> > -     cstate = to_dpu_crtc_state(state);
> > +     struct dpu_crtc_state *cstate = to_dpu_crtc_state(state);
> >
> >       DPU_DEBUG("crtc%d\n", crtc->base.id);
> >
> > @@ -731,14 +701,8 @@ static void dpu_crtc_reset(struct drm_crtc *crtc)
> >   */
> >  static struct drm_crtc_state *dpu_crtc_duplicate_state(struct drm_crtc
> > *crtc)
> >  {
> > -     struct dpu_crtc_state *cstate, *old_cstate;
> > -
> > -     if (!crtc || !crtc->state) {
> > -             DPU_ERROR("invalid argument(s)\n");
> > -             return NULL;
> > -     }
> > +     struct dpu_crtc_state *cstate, *old_cstate =
> > to_dpu_crtc_state(crtc->state);
> >
> > -     old_cstate = to_dpu_crtc_state(crtc->state);
> >       cstate = kmemdup(old_cstate, sizeof(*old_cstate), GFP_KERNEL);
> >       if (!cstate) {
> >               DPU_ERROR("failed to allocate state\n");
> > @@ -754,19 +718,12 @@ static struct drm_crtc_state
> > *dpu_crtc_duplicate_state(struct drm_crtc *crtc)
> >  static void dpu_crtc_disable(struct drm_crtc *crtc,
> >                            struct drm_crtc_state *old_crtc_state)
> >  {
> > -     struct dpu_crtc *dpu_crtc;
> > -     struct dpu_crtc_state *cstate;
> > +     struct dpu_crtc *dpu_crtc = to_dpu_crtc(crtc);
> > +     struct dpu_crtc_state *cstate = to_dpu_crtc_state(crtc->state);
> >       struct drm_encoder *encoder;
> >       unsigned long flags;
> >       bool release_bandwidth = false;
> >
> > -     if (!crtc || !crtc->state) {
> > -             DPU_ERROR("invalid crtc\n");
> > -             return;
> > -     }
> > -     dpu_crtc = to_dpu_crtc(crtc);
> > -     cstate = to_dpu_crtc_state(crtc->state);
> > -
> >       DRM_DEBUG_KMS("crtc%d\n", crtc->base.id);
> >
> >       /* Disable/save vblank irq handling */
> > @@ -825,19 +782,13 @@ static void dpu_crtc_disable(struct drm_crtc
> > *crtc,
> >  static void dpu_crtc_enable(struct drm_crtc *crtc,
> >               struct drm_crtc_state *old_crtc_state)
> >  {
> > -     struct dpu_crtc *dpu_crtc;
> > +     struct dpu_crtc *dpu_crtc = to_dpu_crtc(crtc);
> >       struct drm_encoder *encoder;
> >       bool request_bandwidth = false;
> >
> > -     if (!crtc) {
> > -             DPU_ERROR("invalid crtc\n");
> > -             return;
> > -     }
> > -
> >       pm_runtime_get_sync(crtc->dev->dev);
> >
> >       DRM_DEBUG_KMS("crtc%d\n", crtc->base.id);
> > -     dpu_crtc = to_dpu_crtc(crtc);
> >
> >       drm_for_each_encoder_mask(encoder, crtc->dev,
> > crtc->state->encoder_mask) {
> >               /* in video mode, we hold an extra bandwidth reference
> > @@ -873,9 +824,9 @@ struct plane_state {
> >  static int dpu_crtc_atomic_check(struct drm_crtc *crtc,
> >               struct drm_crtc_state *state)
> >  {
> > -     struct dpu_crtc *dpu_crtc;
> > +     struct dpu_crtc *dpu_crtc = to_dpu_crtc(crtc);
> > +     struct dpu_crtc_state *cstate = to_dpu_crtc_state(state);
> >       struct plane_state *pstates;
> > -     struct dpu_crtc_state *cstate;
> >
> >       const struct drm_plane_state *pstate;
> >       struct drm_plane *plane;
> > @@ -889,16 +840,8 @@ static int dpu_crtc_atomic_check(struct drm_crtc
> > *crtc,
> >       int left_zpos_cnt = 0, right_zpos_cnt = 0;
> >       struct drm_rect crtc_rect = { 0 };
> >
> > -     if (!crtc) {
> > -             DPU_ERROR("invalid crtc\n");
> > -             return -EINVAL;
> > -     }
> > -
> >       pstates = kzalloc(sizeof(*pstates) * DPU_STAGE_MAX * 4, GFP_KERNEL);
> >
> > -     dpu_crtc = to_dpu_crtc(crtc);
> > -     cstate = to_dpu_crtc_state(state);
> > -
> >       if (!state->enable || !state->active) {
> >               DPU_DEBUG("crtc%d -> enable %d, active %d, skip atomic_check\n",
> >                               crtc->base.id, state->enable, state->active);