linux-kernel - [PATCH 9/9] drm/i915/intel_i2c: reuse GMBUS2 value from polling loop

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Message-Id: <1331121050-17857-10-git-send-email-djkurtz@chromium.org>
Date:	Wed,  7 Mar 2012 19:50:50 +0800
From:	Daniel Kurtz <djkurtz@...omium.org>
To:	Keith Packard <keithp@...thp.com>, David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:	Benson Leung <bleung@...omium.org>,
	Yufeng Shen <miletus@...omium.org>,
	Sameer Nanda <snanda@...omium.org>,
	Daniel Kurtz <djkurtz@...omium.org>
Subject: [PATCH 9/9] drm/i915/intel_i2c: reuse GMBUS2 value from polling loop

Save the GMBUS2 value read while polling for state changes, and then
reuse this value when determining for which reason the loops were exited.
This is a small optimization which saves a couple of bus accesses for
memory mapped IO registers.

Note: checkpatch doesn't like this ('assigning in if condition'), but it seems
like the cleanest implementation.

Signed-off-by: Daniel Kurtz <djkurtz@...omium.org>
---
 drivers/gpu/drm/i915/intel_i2c.c |   19 ++++++++++---------
 1 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 41f9ae2..450f2b8 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -244,6 +244,7 @@ gmbus_xfer(struct i2c_adapter *adapter,
 	struct drm_i915_private *dev_priv = adapter->algo_data;
 	int i, reg_offset;
 	int ret = 0;
+	u32 gmbus2 = 0;
 
 	if (bus->force_bit)
 		return intel_i2c_quirk_xfer(dev_priv, bus->force_bit, msgs,
@@ -297,12 +298,12 @@ gmbus_xfer(struct i2c_adapter *adapter,
 			do {
 				u32 val, loop = 0;
 
-				if (wait_for(I915_READ(GMBUS2 + reg_offset) &
+				if (wait_for((gmbus2 = I915_READ(GMBUS2 +
+								 reg_offset)) &
 					     (GMBUS_SATOER | GMBUS_HW_RDY),
 					     50))
 					goto timeout;
-				if (I915_READ(GMBUS2 + reg_offset) &
-				    GMBUS_SATOER)
+				if (gmbus2 & GMBUS_SATOER)
 					goto clear_err;
 
 				val = I915_READ(GMBUS3 + reg_offset);
@@ -336,21 +337,21 @@ gmbus_xfer(struct i2c_adapter *adapter,
 				I915_WRITE(GMBUS3 + reg_offset, val);
 				POSTING_READ(GMBUS2 + reg_offset);
 
-				if (wait_for(I915_READ(GMBUS2 + reg_offset) &
+				if (wait_for((gmbus2 = I915_READ(GMBUS2 +
+								 reg_offset)) &
 					     (GMBUS_SATOER | GMBUS_HW_RDY),
 					     50))
 					goto timeout;
-				if (I915_READ(GMBUS2 + reg_offset) &
-					      GMBUS_SATOER)
+				if (gmbus2 & GMBUS_SATOER)
 					goto clear_err;
 			}
 		}
 
-		if (wait_for(I915_READ(GMBUS2 + reg_offset) &
+		if (wait_for((gmbus2 = I915_READ(GMBUS2 + reg_offset)) &
 			     (GMBUS_SATOER | GMBUS_HW_WAIT_PHASE),
 			     50))
 			goto timeout;
-		if (I915_READ(GMBUS2 + reg_offset) & GMBUS_SATOER)
+		if (gmbus2 & GMBUS_SATOER)
 			goto clear_err;
 	}
 
@@ -366,7 +367,7 @@ clear_err:
 	ret = -ENXIO;
 
 done:
-	if (I915_READ(GMBUS2 + reg_offset) & GMBUS_HW_WAIT_PHASE) {
+	if (gmbus2 & GMBUS_HW_WAIT_PHASE) {
 		I915_WRITE(GMBUS1 + reg_offset,
 			   GMBUS_CYCLE_STOP | GMBUS_SW_RDY);
 		POSTING_READ(GMBUS2 + reg_offset);
-- 
1.7.7.3

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