linux-kernel - [PATCH 4.18 67/88] drm/nouveau/drm/nouveau: Fix bogus drm_kms_helper_poll

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Message-Id: <20180927090308.841540319@linuxfoundation.org>
Date:   Thu, 27 Sep 2018 11:03:48 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Lyude Paul <lyude@...hat.com>,
        Karol Herbst <kherbst@...hat.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Lukas Wunner <lukas@...ner.de>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Ben Skeggs <bskeggs@...hat.com>
Subject: [PATCH 4.18 67/88] drm/nouveau/drm/nouveau: Fix bogus drm_kms_helper_poll_enable() placement

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Lyude Paul <lyude@...hat.com>

commit d77ef138ff572409ab93d492e5e6c826ee6fb21d upstream.

Turns out this part is my fault for not noticing when reviewing
9a2eba337cace ("drm/nouveau: Fix drm poll_helper handling"). Currently
we call drm_kms_helper_poll_enable() from nouveau_display_hpd_work().
This makes basically no sense however, because that means we're calling
drm_kms_helper_poll_enable() every time we schedule the hotplug
detection work. This is also against the advice mentioned in
drm_kms_helper_poll_enable()'s documentation:

 Note that calls to enable and disable polling must be strictly ordered,
 which is automatically the case when they're only call from
 suspend/resume callbacks.

Of course, hotplugs can't really be ordered. They could even happen
immediately after we called drm_kms_helper_poll_disable() in
nouveau_display_fini(), which can lead to all sorts of issues.

Additionally; enabling polling /after/ we call
drm_helper_hpd_irq_event() could also mean that we'd miss a hotplug
event anyway, since drm_helper_hpd_irq_event() wouldn't bother trying to
probe connectors so long as polling is disabled.

So; simply move this back into nouveau_display_init() again. The race
condition that both of these patches attempted to work around has
already been fixed properly in

  d61a5c106351 ("drm/nouveau: Fix deadlock on runtime suspend")

Fixes: 9a2eba337cace ("drm/nouveau: Fix drm poll_helper handling")
Signed-off-by: Lyude Paul <lyude@...hat.com>
Acked-by: Karol Herbst <kherbst@...hat.com>
Acked-by: Daniel Vetter <daniel@...ll.ch>
Cc: Lukas Wunner <lukas@...ner.de>
Cc: Peter Ujfalusi <peter.ujfalusi@...com>
Cc: stable@...r.kernel.org
Signed-off-by: Ben Skeggs <bskeggs@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/gpu/drm/nouveau/nouveau_display.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/nouveau/nouveau_display.c
+++ b/drivers/gpu/drm/nouveau/nouveau_display.c
@@ -355,8 +355,6 @@ nouveau_display_hpd_work(struct work_str
 	pm_runtime_get_sync(drm->dev->dev);

 	drm_helper_hpd_irq_event(drm->dev);
-	/* enable polling for external displays */
-	drm_kms_helper_poll_enable(drm->dev);

 	pm_runtime_mark_last_busy(drm->dev->dev);
 	pm_runtime_put_sync(drm->dev->dev);
@@ -411,6 +409,11 @@ nouveau_display_init(struct drm_device *
 	if (ret)
 		return ret;

+	/* enable connector detection and polling for connectors without HPD
+	 * support
+	 */
+	drm_kms_helper_poll_enable(dev);
+
 	/* enable hotplug interrupts */
 	drm_connector_list_iter_begin(dev, &conn_iter);
 	nouveau_for_each_non_mst_connector_iter(connector, &conn_iter) {