linux-kernel - Re: [PATCH 2/5 v3] drm/bridge: adv7511: Switch to using drm_kms_helper_hotplug

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Message-ID: <7359021.xs7IcXVQ9z@avalon>
Date:   Mon, 16 Jan 2017 17:56:29 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>
Subject: Re: [PATCH 2/5 v3] drm/bridge: adv7511: Switch to using drm_kms_helper_hotplug_event()

On Monday 16 Jan 2017 17:47:46 Laurent Pinchart wrote:
> Hi John,
> 
> Thank you for the patch.
> 
> On Tuesday 03 Jan 2017 11:41:39 John Stultz wrote:
> > In chasing down a previous issue with EDID probing from calling
> > drm_helper_hpd_irq_event() from irq context, Laurent noticed
> > that the DRM documentation suggests that
> > drm_kms_helper_hotplug_event() should be used instead.
> > 
> > Thus this patch replaces drm_helper_hpd_irq_event() with
> > drm_kms_helper_hotplug_event(), which requires we update the
> > connector.status entry and only call _hotplug_event() when the
> > status changes.
> > 
> > Cc: David Airlie <airlied@...ux.ie>
> > Cc: Archit Taneja <architt@...eaurora.org>
> > Cc: Wolfram Sang <wsa+renesas@...g-engineering.com>
> > Cc: Lars-Peter Clausen <lars@...afoo.de>
> > Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > Cc: dri-devel@...ts.freedesktop.org
> > Signed-off-by: John Stultz <john.stultz@...aro.org>
> > ---
> > v3: Update connector.status value and only call __hotplug_event()
> > 
> >     when that status changes, as suggested by Laurent.
> >  
> >  drivers/gpu/drm/bridge/adv7511/adv7511_drv.c | 16 +++++++++++++++-
> >  1 file changed, 15 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> > b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c index 4fcea44..d93d66f
> > 100644
> > --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> > +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> > @@ -405,8 +405,22 @@ static bool adv7511_hpd(struct adv7511 *adv7511)
> > 
> >  static void adv7511_hpd_work(struct work_struct *work)
> >  {
> >  
> >  	struct adv7511 *adv7511 = container_of(work, struct adv7511,
> 
> hpd_work);
> 
> > +	enum drm_connector_status status;
> > +	unsigned int val;
> > +	int ret;
> > +
> > +	ret = regmap_read(adv7511->regmap, ADV7511_REG_STATUS, &val);
> > +	if (ret < 0)
> > +		status = connector_status_disconnected;
> > +	else if (val & ADV7511_STATUS_HPD)
> > +		status = connector_status_connected;
> > +	else
> > +		status = connector_status_disconnected;
> > +
> > +	if (adv7511->connector.status != status)
> > +		drm_kms_helper_hotplug_event(adv7511->connector.dev);
> > 
> > -	drm_helper_hpd_irq_event(adv7511->connector.dev);
> > +	adv7511->connector.status = status;
> 
> Shouldn't you update the status before calling
> drm_kms_helper_hotplug_event() ? Doing it after not only creates a small
> race condition as
> drm_kms_helper_hotplug_event() sends an event to userspace that could result
> in an ioctl call to retrieve the status, but the status is also checked by
> drm_setup_crtcs() called by drm_fb_helper_hotplug_event().

With

        if (adv7511->connector.status != status) {
                adv7511->connector.status = status;
                drm_kms_helper_hotplug_event(adv7511->connector.dev);
        }

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Tested-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> >  }
> >  
> >  static int adv7511_irq_process(struct adv7511 *adv7511, bool process_hpd)

-- 
Regards,

Laurent Pinchart