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authorPeter Rosin <peda@axentia.se>2016-05-04 22:15:29 +0200
committerWolfram Sang <wsa@the-dreams.de>2016-05-04 22:39:17 +0200
commit6ef91fcca8a8ba3df9810a4cc6cd6a9d3f21bf45 (patch)
treec49b93903b331c155cdcdde693bb854e53bf9d95 /include/linux/i2c.h
parentfa96f0cb9b37a1a296d18f7bde63b0910852303e (diff)
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i2c: mux: relax locking of the top i2c adapter during mux-locked muxing
With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Diffstat (limited to 'include/linux/i2c.h')
-rw-r--r--include/linux/i2c.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 50934d6..96a25ae 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -524,6 +524,7 @@ struct i2c_adapter {
/* data fields that are valid for all devices */
struct rt_mutex bus_lock;
+ struct rt_mutex mux_lock;
int timeout; /* in jiffies */
int retries;
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