linux-kernel - Re: [PATCH] drm: drm_probe_helper: Fix output_poll

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Message-ID: <20160829125857.GK10980@phenom.ffwll.local>
Date:   Mon, 29 Aug 2016 14:58:57 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     airlied@...ux.ie, daniel.vetter@...ll.ch,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        ville.syrjala@...ux.intel.com, tomi.valkeinen@...com
Subject: Re: [PATCH] drm: drm_probe_helper: Fix output_poll_work scheduling

On Mon, Aug 29, 2016 at 12:50:22PM +0300, Peter Ujfalusi wrote:
> drm_kms_helper_poll_enable_locked() should check if we have delayed event
> pending and if we have, schedule the work to run without delay.
> 
> Currently the output_poll_work is only scheduled if any of the connectors
> have DRM_CONNECTOR_POLL_CONNECT or DRM_CONNECTOR_POLL_DISCONNECT with
> DRM_OUTPUT_POLL_PERIOD delay. It does not matter if we have delayed event
> already registered to be handled. The detection will be delayd by
> DRM_OUTPUT_POLL_PERIOD in any case.
> Furthermore if none of the connectors are marked as POLL_CONNECT or
> POLL_DISCONNECT because all connectors are either POLL_HPD or they are
> always connected: the output_poll_work will not run at all even if we
> have delayed event marked.
> 
> When none of the connectors require polling, their initial status change
> from unknown to connected/disconnected is not going to be handled until
> the first kms application starts or if we have fb console enabled.
> 
> With this change we can react more quickly to output status changes after
> enabling the poll but most importantly it will correct the behavior when
> none of the connector have POLL_CONNECT or POLL_DISCONNECT flag set - they
> are either POLL_HPD or the .polled is 0. The initial status change is going
> to be handled correctly as well.

Don't we need to set delayed_event somewhere too first? At least I don't
really understand how this speeds things up ... The patch itself looks
like a valid bugfix, but the description confuses me a bit. I think if you
delete the above paragraph (starting with "With this change we can react
...") then it's all good.
-Daniel

> 
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> ---
>  drivers/gpu/drm/drm_probe_helper.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> index a0df377d7d1c..f6b64d7d3528 100644
> --- a/drivers/gpu/drm/drm_probe_helper.c
> +++ b/drivers/gpu/drm/drm_probe_helper.c
> @@ -129,6 +129,7 @@ void drm_kms_helper_poll_enable_locked(struct drm_device *dev)
>  {
>  	bool poll = false;
>  	struct drm_connector *connector;
> +	unsigned long delay = DRM_OUTPUT_POLL_PERIOD;
>  
>  	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
>  
> @@ -141,8 +142,13 @@ void drm_kms_helper_poll_enable_locked(struct drm_device *dev)
>  			poll = true;
>  	}
>  
> +	if (dev->mode_config.delayed_event) {
> +		poll = true;
> +		delay = 0;
> +	}
> +
>  	if (poll)
> -		schedule_delayed_work(&dev->mode_config.output_poll_work, DRM_OUTPUT_POLL_PERIOD);
> +		schedule_delayed_work(&dev->mode_config.output_poll_work, delay);
>  }
>  EXPORT_SYMBOL(drm_kms_helper_poll_enable_locked);
>  
> -- 
> 2.9.3
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch