linux-kernel - [PATCH] drm/i915: Flush writes to GMBUS registers

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Message-Id: <1363605185-4030-1-git-send-email-chris@chris-wilson.co.uk>
Date:	Mon, 18 Mar 2013 11:13:05 +0000
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	linux-kernel@...r.kernel.org
Cc:	intel-gfx@...ts.freedesktop.org,
	Chris Wilson <chris@...is-wilson.co.uk>,
	Shawn Starr <shawn.starr@...ers.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Daniel Vetter <daniel.vetter@...ll.ch>
Subject: [PATCH] drm/i915: Flush writes to GMBUS registers

If we do not complete the writes to the GMBUS registers, they remain
active for an indefinite period of time afterwards, even causing
spurious interrupts on gm45.

Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
Link: http://lkml.kernel.org/r/alpine.LNX.2.00.1303151424140.9529@pobox.suse.cz
Cc: Shawn Starr <shawn.starr@...ers.com>
Cc: Jiri Kosina <jkosina@...e.cz>
Cc: Daniel Vetter <daniel.vetter@...ll.ch>
---
 drivers/gpu/drm/i915/intel_i2c.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index acf8aec..ca6c17e 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -64,6 +64,7 @@ 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);
+	POSTING_READ(dev_priv->gpio_mmio_base + GMBUS4);
 }
 
 static void intel_i2c_quirk_set(struct drm_i915_private *dev_priv, bool enable)
@@ -232,6 +233,7 @@ gmbus_wait_hw_status(struct drm_i915_private *dev_priv,
 	finish_wait(&dev_priv->gmbus_wait_queue, &wait);
 
 	I915_WRITE(GMBUS4 + reg_offset, 0);
+	POSTING_READ(GMBUS4 + reg_offset);
 
 	if (gmbus2 & GMBUS_SATOER)
 		return -ENXIO;
@@ -257,6 +259,7 @@ gmbus_wait_idle(struct drm_i915_private *dev_priv)
 	ret = wait_event_timeout(dev_priv->gmbus_wait_queue, C, 10);
 
 	I915_WRITE(GMBUS4 + reg_offset, 0);
+	POSTING_READ(GMBUS4 + reg_offset);
 
 	if (ret)
 		return 0;
@@ -486,6 +489,7 @@ timeout:
 	ret = i2c_bit_algo.master_xfer(adapter, msgs, num);
 
 out:
+	POSTING_READ(GMBUS0 + dev_priv->gpio_mmio_base);
 	mutex_unlock(&dev_priv->gmbus_mutex);
 	return ret;
 }
-- 
1.7.10.4

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