[PATCH v3 6/9] drm/i915: Make use of indexed write GMBUS feature

[Sean Paul]

This patch enables the indexed write feature of the GMBUS to concatenate
2 consecutive messages into one. The criteria for an indexed write is
that both messages are writes, the first is length == 1, and the second
is length > 0. The first message is sent out by the GMBUS as the slave
command, and the second one is sent via the GMBUS FIFO as usual.

Changes in v3:
- Added to series

Suggested-by: Ville SyrjÃlà <ville.syrjala@xxxxxxxxxxxxxxx>
Signed-off-by: Sean Paul <seanpaul@xxxxxxxxxxxx>
---
 drivers/gpu/drm/i915/intel_i2c.c | 39 ++++++++++++++++++++++++++++++++++-----
 1 file changed, 34 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 49fdf09f9919..7399009aee0a 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -373,7 +373,8 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
 
 static int
 gmbus_xfer_write_chunk(struct drm_i915_private *dev_priv,
-		       unsigned short addr, u8 *buf, unsigned int len)
+		       unsigned short addr, u8 *buf, unsigned int len,
+		       u32 gmbus1_index)
 {
 	unsigned int chunk_size = len;
 	u32 val, loop;
@@ -386,7 +387,7 @@ gmbus_xfer_write_chunk(struct drm_i915_private *dev_priv,
 
 	I915_WRITE_FW(GMBUS3, val);
 	I915_WRITE_FW(GMBUS1,
-		      GMBUS_CYCLE_WAIT |
+		      gmbus1_index | GMBUS_CYCLE_WAIT |
 		      (chunk_size << GMBUS_BYTE_COUNT_SHIFT) |
 		      (addr << GMBUS_SLAVE_ADDR_SHIFT) |
 		      GMBUS_SLAVE_WRITE | GMBUS_SW_RDY);
@@ -409,7 +410,8 @@ gmbus_xfer_write_chunk(struct drm_i915_private *dev_priv,
 }
 
 static int
-gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
+gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
+		 u32 gmbus1_index)
 {
 	u8 *buf = msg->buf;
 	unsigned int tx_size = msg->len;
@@ -419,7 +421,8 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
 	do {
 		len = min(tx_size, GMBUS_BYTE_COUNT_MAX);
 
-		ret = gmbus_xfer_write_chunk(dev_priv, msg->addr, buf, len);
+		ret = gmbus_xfer_write_chunk(dev_priv, msg->addr, buf, len,
+					     gmbus1_index);
 		if (ret)
 			return ret;
 
@@ -430,6 +433,14 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
 	return 0;
 }
 
+static int
+gmbus_xfer_index_write(struct drm_i915_private *dev_priv, u8 cmd,
+		       struct i2c_msg *msg)
+{
+	u8 gmbus1_index = GMBUS_CYCLE_INDEX | (cmd << GMBUS_SLAVE_INDEX_SHIFT);
+	return gmbus_xfer_write(dev_priv, msg, gmbus1_index);
+}
+
 /*
  * The gmbus controller can combine a 1 or 2 byte write with a read that
  * immediately follows it by using an "INDEX" cycle.
@@ -444,6 +455,20 @@ gmbus_is_index_read(struct i2c_msg *msgs, int i, int num)
 		(msgs[i + 1].flags & I2C_M_RD));
 }
 
+/*
+ * The gmbus controller can combine a 2-msg write into a single write that
+ * immediately follows it by using an "INDEX" cycle.
+ */
+static bool
+gmbus_is_index_write(struct i2c_msg *msgs, int i, int num)
+{
+	return (i + 1 < num &&
+		msgs[i].addr == msgs[i + 1].addr &&
+		!(msgs[i].flags & I2C_M_RD) &&
+		!(msgs[i + 1].flags & I2C_M_RD) &&
+		(msgs[i].len == 1 || msgs[i + 1].len > 0));
+}
+
 static int
 gmbus_xfer_index_read(struct drm_i915_private *dev_priv, struct i2c_msg *msgs)
 {
@@ -489,10 +514,14 @@ do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
 		if (gmbus_is_index_read(msgs, i, num)) {
 			ret = gmbus_xfer_index_read(dev_priv, &msgs[i]);
 			inc = 2; /* an index read is two msgs */
+		} else if (gmbus_is_index_write(msgs, i, num)) {
+			ret = gmbus_xfer_index_write(dev_priv, msgs[i].buf[0],
+					&msgs[i + 1]);
+			inc = 2; /* an index write is two msgs */
 		} else if (msgs[i].flags & I2C_M_RD) {
 			ret = gmbus_xfer_read(dev_priv, &msgs[i], 0);
 		} else {
-			ret = gmbus_xfer_write(dev_priv, &msgs[i]);
+			ret = gmbus_xfer_write(dev_priv, &msgs[i], 0);
 		}
 
 		if (!ret)
-- 
2.15.0.531.g2ccb3012c9-goog