[PATCH] drm/msm: dpu: Don't enable vblank interrupts in irq_control

[Sean Paul]

On Fri, Dec 07, 2018 at 01:16:54PM -0800, Abhinav Kumar wrote:
> On 2018-12-07 09:16, Sean Paul wrote:
> > From: Sean Paul <seanpaul at chromium.org>
> > 
> > The irq_control function is called upon encoder enable/disable and turns
> > on/off the vblank interrupts. Unfortunately, it enables them when the
> > drm code is not expecting them to be on. As a result, we can get into
> > nasty locking situations.
> > 
> > vblank interrupts should be solely managed by the drm core via
> > control_vblank_irq(). This patch removes the vblank irq handling from
> > irq_control.
> > 
> > Here's some tracing before this patch:
> > -- CRTC is enabled, irq_control is called, drm_vblank reference is 0
> >    25.078455: dpu_crtc_enable: id:46 enable:true state{enabled:false}
> > -- vblank irqs incorrectly firing, drm_crtc_handle_vblank is called from
> > them
> >    25.290067: dpu_crtc_vblank_cb: id=46
> >    25.306691: dpu_crtc_vblank_cb: id=46
> > -- drm core enables vblank interrupts, drm_vblank_reference > 0
> >    25.311527: dpu_crtc_vblank: id:46 enable:true state{enabled:true}
> > -- vblank irqs continue (correctly)
> >    25.323351: dpu_crtc_vblank_cb: id=46
> >    25.340033: dpu_crtc_vblank_cb: id=46
> >    25.356701: dpu_crtc_vblank_cb: id=46
> > 
> > And after this patch:
> > -- CRTC is enabled, irq_control does not enable vblank interrupts
> >   123.861353: dpu_crtc_enable: id:46 enable:true state{enabled:false}
> > -- drm core enables vblank, we enable the irq
> >   124.192916: dpu_crtc_vblank: id:46 enable:true state{enabled:true}
> > -- vblank irqs start at the correct time
> >   124.200548: dpu_crtc_vblank_cb: id=46
> >   124.217195: dpu_crtc_vblank_cb: id=46
> >   124.233848: dpu_crtc_vblank_cb: id=46
> > 
> > Signed-off-by: Sean Paul <seanpaul at chromium.org>
> 
> With this change "FROMLIST: drm/msm: Grab a vblank reference when waiting
> for commit_done"
> in place, this patch looks fine to me as we are protected to disable vblank
> right after commit hence cases such as idle power collapse for smart panels
> ideally
> shouldnt get impacted.
> 
> However, since we are not validating smart panels do we want to remove
> changes to dpu_encoder_phys_cmd.c and just keep it for video mode?

We really don't want the vblank handler running when it's not supposed
to. So having the irq always enabled may be covering up another bug in
cmd mode, but I'd much rather fix this now and deal with regressions
if they surface than leave a known issue in the code.

Sean

> 
> > ---
> >  drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c | 2 --
> >  drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c | 6 ------
> >  2 files changed, 8 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c
> > b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c
> > index 99ab5ca9bed3..c9eaa3516e9a 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c
> > @@ -339,7 +339,6 @@ static void
> > dpu_encoder_phys_cmd_irq_control(struct dpu_encoder_phys *phys_enc,
> >  	if (enable) {
> >  		dpu_encoder_helper_register_irq(phys_enc, INTR_IDX_PINGPONG);
> >  		dpu_encoder_helper_register_irq(phys_enc, INTR_IDX_UNDERRUN);
> > -		dpu_encoder_phys_cmd_control_vblank_irq(phys_enc, true);
> > 
> >  		if (dpu_encoder_phys_cmd_is_master(phys_enc))
> >  			dpu_encoder_helper_register_irq(phys_enc,
> > @@ -350,7 +349,6 @@ static void
> > dpu_encoder_phys_cmd_irq_control(struct dpu_encoder_phys *phys_enc,
> >  					INTR_IDX_CTL_START);
> > 
> >  		dpu_encoder_helper_unregister_irq(phys_enc, INTR_IDX_UNDERRUN);
> > -		dpu_encoder_phys_cmd_control_vblank_irq(phys_enc, false);
> >  		dpu_encoder_helper_unregister_irq(phys_enc, INTR_IDX_PINGPONG);
> >  	}
> >  }
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> > b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> > index acdab5b0db18..e3125a1ab3dc 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> > @@ -706,7 +706,6 @@ static void
> > dpu_encoder_phys_vid_irq_control(struct dpu_encoder_phys *phys_enc,
> >  		bool enable)
> >  {
> >  	struct dpu_encoder_phys_vid *vid_enc;
> > -	int ret;
> > 
> >  	if (!phys_enc)
> >  		return;
> > @@ -719,13 +718,8 @@ static void
> > dpu_encoder_phys_vid_irq_control(struct dpu_encoder_phys *phys_enc,
> >  			    atomic_read(&phys_enc->vblank_refcount));
> > 
> >  	if (enable) {
> > -		ret = dpu_encoder_phys_vid_control_vblank_irq(phys_enc, true);
> > -		if (ret)
> > -			return;
> > -
> >  		dpu_encoder_helper_register_irq(phys_enc, INTR_IDX_UNDERRUN);
> >  	} else {
> > -		dpu_encoder_phys_vid_control_vblank_irq(phys_enc, false);
> >  		dpu_encoder_helper_unregister_irq(phys_enc, INTR_IDX_UNDERRUN);
> >  	}
> >  }

-- 
Sean Paul, Software Engineer, Google / Chromium OS