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

[Abhinav Kumar <abhinavk-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

On 2018-12-07 09:16, Sean Paul wrote:
> From: Sean Paul <seanpaul@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@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?

> ---
>  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);
>  	}
>  }
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