[Intel-gfx] [PATCH 5/7] drm/i915: Error checks in gen6_set_rps

[Ben Widawsky]

With the new "standardized" sysfs interfaces we need to be a bit more
careful about setting the RPS values.

Because the sysfs code and the rps workqueue can run at the same time,
if the sysfs setter wins the race to the mutex, the workqueue can come
in and set a value which is out of range (ie. we're no longer protecting
by RPINTLIM).

I was not able to actually make this error occur in testing.

Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/i915/i915_irq.c | 8 +++++++-
 drivers/gpu/drm/i915/intel_pm.c | 2 ++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index d601013..e34b7d4 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -382,7 +382,13 @@ static void gen6_pm_rps_work(struct work_struct *work)
 	else
 		new_delay = dev_priv->rps.cur_delay - 1;
 
-	gen6_set_rps(dev_priv->dev, new_delay);
+	/* sysfs frequency interfaces may have snuck in while servicing the
+	 * interrupt
+	 */
+	if (!(new_delay > dev_priv->rps.max_delay ||
+	      new_delay < dev_priv->rps.min_delay)) {
+		gen6_set_rps(dev_priv->dev, new_delay);
+	}
 
 	mutex_unlock(&dev_priv->dev->struct_mutex);
 }
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 4e86037..82ca172 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -2324,6 +2324,8 @@ void gen6_set_rps(struct drm_device *dev, u8 val)
 	u32 limits = gen6_rps_limits(dev_priv, &val);
 
 	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
+	WARN_ON(val > dev_priv->rps.max_delay);
+	WARN_ON(val < dev_priv->rps.min_delay);
 
 	if (val == dev_priv->rps.cur_delay)
 		return;
-- 
1.7.12