Implement board-level I2C arbitration

Add a way for boards to permit or deny access to the I2C port. This
works in a board-specific manner.

All I2C master traffic requires that board_i2c_claim() be called
first. A dummy function is provided for boards which do not require
this.

BUG=chrome-os-partner:10888
TEST=manual:
build for all boards
boot on snow (cannot test i2c as it is broken)

Change-Id: I786d4ae17f1d798faf13b303b5389679fb6720cb
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/26141

2 files changed, 55 insertions, 0 deletions

diff --git a/chip/stm32/i2c.c b/chip/stm32/i2c.c
index 68305e0cdd..bf34f5a466 100644
--- a/chip/stm32/i2c.c
+++ b/chip/stm32/i2c.c
@@ -70,6 +70,23 @@ static inline void disable_ack(int port)
 	STM32_I2C_CR1(port) &= ~(1 << 10);
 }
 
+int __board_i2c_claim(int port)
+{
+	return 0;
+}
+
+int board_i2c_claim(int port)
+	__attribute__((weak, alias("__board_i2c_claim")));
+
+
+void __board_i2c_release(int port)
+{
+}
+
+void board_i2c_release(int port)
+	__attribute__((weak, alias("__board_i2c_release")));
+
+
 static int wait_tx(int port)
 {
 	static timestamp_t deadline;
@@ -554,6 +571,12 @@ static int i2c_xfer(int port, int slave_addr, uint8_t *out, int out_bytes,
 	ASSERT(in || !in_bytes);
 
 	mutex_lock(&i2c_mutex);
+
+	if (board_i2c_claim(port)) {
+		rv = EC_ERROR_BUSY;
+		goto err_claim;
+	}
+
 	disable_i2c_interrupt(port);
 
 	rv = i2c_master_transmit(port, slave_addr, out, out_bytes,
@@ -563,6 +586,10 @@ static int i2c_xfer(int port, int slave_addr, uint8_t *out, int out_bytes,
 	handle_i2c_error(port, rv);
 
 	enable_i2c_interrupt(port);
+
+	board_i2c_release(port);
+
+err_claim:
 	mutex_unlock(&i2c_mutex);
 
 	return rv;
diff --git a/include/i2c.h b/include/i2c.h
index 726ebb641a..dbf933e102 100644
--- a/include/i2c.h
+++ b/include/i2c.h
@@ -48,4 +48,32 @@ int i2c_write8(int port, int slave_addr, int offset, int data);
 int i2c_read_string(int port, int slave_addr, int offset, uint8_t *data,
 			int len);
 
+/**
+ * Claim an I2C port for use in master mode
+ *
+ * If this function succeed, then you must later call board_i2c_release()
+ * to release the claim.
+ *
+ * This function may optionally be implemented by a board file. If provided
+ * then it should check the port number and arbitrate as needed.
+ *
+ * This function will not be called to claim an already-claimed port.
+ *
+ * @param port	Port to claim (0 for first, 1 for second, etc.)
+ * @return 0 if claimed successfully, -1 if it is in use
+ */
+int board_i2c_claim(int port);
+
+/**
+ * Release an I2C port (after previously being claimed)
+ *
+ * This function may optionally be implemented by a board file. If provided
+ * then it should check the port number and arbitrate as needed.
+ *
+ * This function will not be called to release an already-released port.
+ *
+ * @param port	Port to claim (0 for first, 1 for second, etc.)
+ */
+void board_i2c_release(int port);
+
 #endif  /* __CROS_EC_I2C_H */