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 11:31:44 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.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 Mon, Jan 16, 2017 at 7:56 AM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> 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>

Thanks so much for catching this! I'll respin the patches with this
fix and resend a v4.

thanks again!
-john