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Subject[PATCH 7/9] drm/i915/intel_i2c: use WAIT cycle, not STOP
Date
The i915 is only able to generate a STOP cycle (i.e. finalize an i2c
transaction) during a DATA or WAIT phase. In other words, the
controller rejects a STOP requested as part of the first transaction in a
sequence.

Thus, for the first transaction we must always use a WAIT cycle, detect
when the device has finished (and is in a WAIT phase), and then either
start the next transaction, or, if there are no more transactions,
generate a STOP cycle.

Note: Theoretically, the last transaction of a multi-transaction sequence
could initiate a STOP cycle. However, this slight optimization is left
for another patch. We return -ETIMEDOUT if the hardware doesn't
deactivate after the STOP cycle.

This patch also takes advantage (in the write path) of the double-buffered
GMBUS3 data register by writing two 4-byte words before the first wait for
HW_RDY.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
---
drivers/gpu/drm/i915/intel_i2c.c | 42 +++++++++++++++++++++++++------------
1 files changed, 28 insertions(+), 14 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 2cdd531..c3d8c70 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -261,7 +261,7 @@ gmbus_xfer(struct i2c_adapter *adapter,

if (msgs[i].flags & I2C_M_RD) {
I915_WRITE(GMBUS1 + reg_offset,
- GMBUS_CYCLE_WAIT | (i + 1 == num ? GMBUS_CYCLE_STOP : 0) |
+ GMBUS_CYCLE_WAIT |
(len << GMBUS_BYTE_COUNT_SHIFT) |
(msgs[i].addr << GMBUS_SLAVE_ADDR_SHIFT) |
GMBUS_SLAVE_READ | GMBUS_SW_RDY);
@@ -273,7 +273,8 @@ gmbus_xfer(struct i2c_adapter *adapter,
(GMBUS_SATOER | GMBUS_HW_RDY),
50))
goto timeout;
- if (I915_READ(GMBUS2 + reg_offset) & GMBUS_SATOER)
+ if (I915_READ(GMBUS2 + reg_offset) &
+ GMBUS_SATOER)
goto clear_err;

val = I915_READ(GMBUS3 + reg_offset);
@@ -292,20 +293,13 @@ gmbus_xfer(struct i2c_adapter *adapter,

I915_WRITE(GMBUS3 + reg_offset, val);
I915_WRITE(GMBUS1 + reg_offset,
- (i + 1 == num ? GMBUS_CYCLE_STOP : GMBUS_CYCLE_WAIT) |
+ GMBUS_CYCLE_WAIT |
(msgs[i].len << GMBUS_BYTE_COUNT_SHIFT) |
(msgs[i].addr << GMBUS_SLAVE_ADDR_SHIFT) |
GMBUS_SLAVE_WRITE | GMBUS_SW_RDY);
POSTING_READ(GMBUS2 + reg_offset);

while (len) {
- if (wait_for(I915_READ(GMBUS2 + reg_offset) &
- (GMBUS_SATOER | GMBUS_HW_RDY),
- 50))
- goto timeout;
- if (I915_READ(GMBUS2 + reg_offset) & GMBUS_SATOER)
- goto clear_err;
-
val = loop = 0;
do {
val |= *buf++ << (8 * loop);
@@ -313,11 +307,18 @@ 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) &
+ (GMBUS_SATOER | GMBUS_HW_RDY),
+ 50))
+ goto timeout;
+ if (I915_READ(GMBUS2 + reg_offset) &
+ GMBUS_SATOER)
+ goto clear_err;
}
}

- if (i + 1 < num &&
- wait_for(I915_READ(GMBUS2 + reg_offset) &
+ if (wait_for(I915_READ(GMBUS2 + reg_offset) &
(GMBUS_SATOER | GMBUS_HW_WAIT_PHASE),
50))
goto timeout;
@@ -337,9 +338,22 @@ clear_err:
ret = -ENXIO;

done:
- /* Mark the GMBUS interface as disabled. We will re-enable it at the
- * start of the next xfer, till then let it sleep.
+ if (I915_READ(GMBUS2 + reg_offset) & GMBUS_HW_WAIT_PHASE) {
+ I915_WRITE(GMBUS1 + reg_offset,
+ GMBUS_CYCLE_STOP | GMBUS_SW_RDY);
+ POSTING_READ(GMBUS2 + reg_offset);
+ }
+
+ /* Mark the GMBUS interface as disabled after waiting for idle.
+ * We will re-enable it at the start of the next xfer,
+ * till then let it sleep.
*/
+ if (wait_for((I915_READ(GMBUS2 + reg_offset) & GMBUS_ACTIVE) == 0,
+ 10)) {
+ DRM_INFO("GMBUS [%s] timed out waiting for IDLE\n",
+ adapter->name);
+ ret = -ETIMEDOUT;
+ }
I915_WRITE(GMBUS0 + reg_offset, 0);

mutex_unlock(&dev_priv->gmbus_mutex);
--
1.7.7.3


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