[PATCH v7 1/2] i2c: algo: bit: Allow to skip bit test

[Markus Stockhausen]

An I2C bus can make use of shared resources. E.g. two GPIO based buses
that share a single SCL line. To synchronize access to the bus the driver
might use locking with the help of i2c_lock_operations(). While this
works for normal transfers it is not available during initialization.

Especially if i2c-algo-bit module is loaded with parameter bit_test
it will issue some basic sanity checks that will access the bus without
locking. This might interfere badly with concurrent transfers. Even
if these are well synchronized via locks.

Allow the consumer of an algorithm to override if the bit_test is allowed
or not. For this add a new boolean attribute named skip_bit_test to
i2c_algo_bit_data. If set the test is not run.

Signed-off-by: Markus Stockhausen <markus.stockhausen@xxxxxx>
---
 drivers/i2c/algos/i2c-algo-bit.c | 2 +-
 include/linux/i2c-algo-bit.h     | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/algos/i2c-algo-bit.c b/drivers/i2c/algos/i2c-algo-bit.c
index d1d9a6c1a1e2..7ca565cbff5b 100644
--- a/drivers/i2c/algos/i2c-algo-bit.c
+++ b/drivers/i2c/algos/i2c-algo-bit.c
@@ -639,7 +639,7 @@ static int __i2c_bit_add_bus(struct i2c_adapter *adap,
 	struct i2c_algo_bit_data *bit_adap = adap->algo_data;
 	int ret;
 
-	if (bit_test) {
+	if (bit_test && !bit_adap->skip_bit_test) {
 		ret = test_bus(adap);
 		if (bit_test >= 2 && ret < 0)
 			return -ENODEV;
diff --git a/include/linux/i2c-algo-bit.h b/include/linux/i2c-algo-bit.h
index 7fd5575a368f..c4c43aec1e67 100644
--- a/include/linux/i2c-algo-bit.h
+++ b/include/linux/i2c-algo-bit.h
@@ -34,6 +34,7 @@ struct i2c_algo_bit_data {
 				   maximum 50 us for SMBus */
 	int timeout;		/* in jiffies */
 	bool can_do_atomic;	/* callbacks don't sleep, we can be atomic */
+	bool skip_bit_test;	/* override bit_test module parameter */
 };
 
 int i2c_bit_add_bus(struct i2c_adapter *);
-- 
2.54.0