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

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Date:   Mon, 16 Jan 2017 17:47:46 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Archit Taneja <architt@...eaurora.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 2/5 v3] drm/bridge: adv7511: Switch to using drm_kms_helper_hotplug_event()

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().

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

-- 
Regards,

Laurent Pinchart