[PATCH] drm/i915: stop using GMBUS IRQs on Gen4 chips (was Re: [3.9-rc1] irq 16: nobody cared (was [3.9-rc1] very poor interrupt responses))

[Jiri Kosina]

Okay, so I think that for 3.9 we want the patch below, and if eventually 
hardware root cause / workaround is found for GM45, we can have it merged 
later.



From: Jiri Kosina <jkosina at suse.cz>
Subject: [PATCH] drm/i915: stop using GMBUS IRQs on Gen4 chips

Commit 28c70f162 ("drm/i915: use the gmbus irq for waits") switched to
using GMBUS irqs instead of GPIO bit-banging for chipset generations 4
and above.

It turns out though that on many systems this leads to spurious interrupts
being generated, long after the register write to disable the IRQs has been
issued.

Flushing of the register writes by POSTING_READ() directly after the register
write doesn't work either.

Disable using of GMBUS IRQs on Gen4 systems before the root cause is found and
revert back to old behavior.

Also be more careful about not issuing GMBUS4 register reads in 
gmbus_wait_hw_status() if we are not using GMBUS IRQs.

Signed-off-by: Jiri Kosina <jkosina at suse.cz>
---
 drivers/gpu/drm/i915/intel_i2c.c |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index acf8aec..8638036 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -58,12 +58,14 @@ to_intel_gmbus(struct i2c_adapter *i2c)
 	return container_of(i2c, struct intel_gmbus, adapter);
 }
 
+#define HAS_GMBUS_IRQ(dev) (INTEL_INFO(dev)->gen >= 5)
 void
 intel_i2c_reset(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	I915_WRITE(dev_priv->gpio_mmio_base + GMBUS0, 0);
-	I915_WRITE(dev_priv->gpio_mmio_base + GMBUS4, 0);
+	if (HAS_GMBUS_IRQ(dev))
+		I915_WRITE(dev_priv->gpio_mmio_base + GMBUS4, 0);
 }
 
 static void intel_i2c_quirk_set(struct drm_i915_private *dev_priv, bool enable)
@@ -203,7 +205,6 @@ intel_gpio_setup(struct intel_gmbus *bus, u32 pin)
 	algo->data = bus;
 }
 
-#define HAS_GMBUS_IRQ(dev) (INTEL_INFO(dev)->gen >= 4)
 static int
 gmbus_wait_hw_status(struct drm_i915_private *dev_priv,
 		     u32 gmbus2_status,
@@ -214,6 +215,13 @@ gmbus_wait_hw_status(struct drm_i915_private *dev_priv,
 	u32 gmbus2 = 0;
 	DEFINE_WAIT(wait);
 
+	if (!HAS_GMBUS_IRQ(dev_priv->dev)) {
+		int ret;
+		ret = wait_for((gmbus2 = I915_READ(GMBUS2 + reg_offset)) &
+				(GMBUS_SATOER | gmbus2_status),
+				50);
+		return ret;
+	}
 	/* Important: The hw handles only the first bit, so set only one! Since
 	 * we also need to check for NAKs besides the hw ready/idle signal, we
 	 * need to wake up periodically and check that ourselves. */

-- 
Jiri Kosina
SUSE Labs