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 21:16:41 +0300
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Lyude Paul <lyude@...hat.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, 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.

-- 
Ville Syrjälä
Intel