linux-kernel - Re: [PATCH v2 RESEND] drm/komeda: Workaround for broken FLIP_COMPLETE timestamps

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Date:   Tue, 1 Oct 2019 14:42:56 +0000
From:   Ayan Halder <Ayan.Halder@....com>
To:     Mihail Atanassov <Mihail.Atanassov@....com>
CC:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        Liviu Dudau <Liviu.Dudau@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "james qian wang (Arm Technology China)" <james.qian.wang@....com>,
        nd <nd@....com>
Subject: Re: [PATCH v2 RESEND] drm/komeda: Workaround for broken FLIP_COMPLETE
 timestamps

On Tue, Oct 01, 2019 at 02:21:40PM +0000, Mihail Atanassov wrote:
> When initially turning a crtc on, drm_reset_vblank_timestamp will
> set the vblank timestamp to 0 for any driver that doesn't provide
> a ->get_vblank_timestamp() hook.
> 
> Unfortunately, the FLIP_COMPLETE event depends on that timestamp,
> and the only way to regenerate a valid one is to have vblank
> interrupts enabled and have a valid in-ISR call to
> drm_crtc_handle_vblank.
> 
> Additionally, if the user doesn't request vblanks but _does_ request
> FLIP_COMPLETE events, we still don't have a good timestamp: it'll be the
> same stamp as the last vblank one.
> 
> Work around the issue by always enabling vblanks when the CRTC is on.
> Reducing the amount of time that PL0 has to be unmasked would be nice to
> fix at a later time.
> 
> Changes since v1 [https://patchwork.freedesktop.org/patch/331727/]:
>  - moved drm_crtc_vblank_put call to the ->atomic_disable() hook
> 
> Cc: Daniel Vetter <daniel@...ll.ch>
> Cc: Liviu Dudau <Liviu.Dudau@....com>
> Signed-off-by: Mihail Atanassov <mihail.atanassov@....com>
> Reviewed-by: James Qian Wang (Arm Technology China) <james.qian.wang@....com>

Pushed to drm-misc-next f59769c52cd7d158df53487ec2936f5592073340

Thanks,
Ayan
> ---
>  drivers/gpu/drm/arm/display/komeda/komeda_crtc.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> index 9ca5dbfd0723..75263d8cd0bd 100644
> --- a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> @@ -249,6 +249,7 @@ komeda_crtc_atomic_enable(struct drm_crtc *crtc,
>  {
>  	komeda_crtc_prepare(to_kcrtc(crtc));
>  	drm_crtc_vblank_on(crtc);
> +	WARN_ON(drm_crtc_vblank_get(crtc));
>  	komeda_crtc_do_flush(crtc, old);
>  }
>  
> @@ -341,6 +342,7 @@ komeda_crtc_atomic_disable(struct drm_crtc *crtc,
>  		komeda_crtc_flush_and_wait_for_flip_done(kcrtc, disable_done);
>  	}
>  
> +	drm_crtc_vblank_put(crtc);
>  	drm_crtc_vblank_off(crtc);
>  	komeda_crtc_unprepare(kcrtc);
>  }
> -- 
> 2.23.0
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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