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Date: Tue, 8 Sep 2020 13:11:56 -0700
From: Rob Clark <robdclark@...il.com>
To: Abhinav Kumar <abhinavk@...eaurora.org>
Cc: dri-devel <dri-devel@...ts.freedesktop.org>,
linux-arm-msm <linux-arm-msm@...r.kernel.org>,
freedreno <freedreno@...ts.freedesktop.org>,
Rob Clark <robdclark@...omium.org>,
Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>,
Drew Davenport <ddavenport@...omium.org>,
Kalyan Thota <kalyan_t@...eaurora.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
Hongbo Yao <yaohongbo@...wei.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-arm-msm-owner@...r.kernel.org
Subject: Re: [PATCH 2/2] drm/msm/dpu: clean up some impossibilities
On Tue, Sep 8, 2020 at 12:44 PM <abhinavk@...eaurora.org> wrote:
>
> On 2020-09-07 10:04, Rob Clark wrote:
> > From: Rob Clark <robdclark@...omium.org>
> >
> > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > ---
> > 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);
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