linux-kernel - Re: [PATCH] drm/probe_helper: Don't bother probing when connectors are forced off

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Date:   Mon, 17 Sep 2018 17:12:04 -0400
From:   Lyude Paul <lyude@...hat.com>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     dri-devel@...ts.freedesktop.org, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...ux.ie>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/probe_helper: Don't bother probing when connectors
 are forced off

On Mon, 2018-09-17 at 21:16 +0300, Ville Syrjälä wrote:
> On Mon, Sep 17, 2018 at 02:10:02PM -0400, Lyude Paul wrote:
> > On Mon, 2018-09-17 at 20:55 +0300, Ville Syrjälä wrote:
> > > On Mon, Sep 17, 2018 at 01:43:44PM -0400, Lyude Paul wrote:
> > > > Userspace asked them to be forced off, so why would we care about what a
> > > > probe tells us?
> > > 
> > > I believe there should be force checks in the callers already.
> > > Or are we missing some?
> > 
> > JFYI, what triggered me to send this patch are these error messages that
> > come
> > from nouveau when a hotplug happens on a port that we've forced off:
> > 
> > [ 1903.918104] nouveau 0000:01:00.0: DRM: DDC responded, but no EDID for DP-
> > 2
> > [ 1903.918123] [drm:drm_helper_hpd_irq_event [drm_kms_helper]]
> > [CONNECTOR:61:DP-2] status updated from disconnected to disconnected
> > 
> > That being said; I'm sure there are probably some checks missing, but I
> > don't
> > really see the purpose in calling the driver's probe functions at all if
> > they're
> > just supposed to return the status we forced.
> 
> Digging through my cobweb ridden local git repository I found this:
> 
> commit bbd17813a7c7d0210c619365707044d0fb29e3f0
> Author: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> Date:   Mon Jun 10 15:28:55 2013 +0300
> 
>     drm: Ignore forced connectors in drm_helper_hpd_irq_event()
>     
>     drm_helper_hpd_irq_event() calls the connector's .detect() function
>     even for forced connectors. If the returned status doesn't match the
>     forced status, we will send the hotplug event, causing userspace to
>     re-probe all the connectors. Eventually we should end up back where
>     we started when drm_helper_probe_single_connector_modes() overwrites
>     the connector status with the forced status.
>     
>     We can avoid all that pointles work if we just skip forced connectors
>     in drm_helper_hpd_irq_event().
>     
>     Signed-off-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> 
> diff --git a/drivers/gpu/drm/drm_crtc_helper.c
> b/drivers/gpu/drm/drm_crtc_helper.c
> index ed1334e27c33..4fc2ad76c107 100644
> --- a/drivers/gpu/drm/drm_crtc_helper.c
> +++ b/drivers/gpu/drm/drm_crtc_helper.c
> @@ -1086,6 +1086,10 @@ void drm_helper_hpd_irq_event(struct drm_device *dev)
>  	mutex_lock(&dev->mode_config.mutex);
>  	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
>  
> +		/* Ignore forced connectors. */
> +		if (connector->force)
> +			continue;
> +
>  		/* Only handle HPD capable connectors. */
>  		if (!(connector->polled & DRM_CONNECTOR_POLL_HPD))
>  			continue;
> 
> 
> I guess I never sent it out.

Ahhh, to be honest though this patch isn't really enough.
drm_helper_hpd_irq_event() isn't going to be used by all drivers (I may remove
some usage of it in nouveau in the near future, even) so I still think it would
be a better idea to just add this into drm_helper_probe_detect() and
drm_helper_probe_detect_ctx() so everything gets covered

>