diff options
| author | Wolfram Sang <wsa+renesas@sang-engineering.com> | 2019-03-03 16:03:14 +0100 |
|---|---|---|
| committer | Wolfram Sang <wsa@the-dreams.de> | 2019-03-12 14:09:33 +0100 |
| commit | 7ce98a5591d292c7630e2c6804ba0818a75a0f86 (patch) | |
| tree | 94d005b4d29d247b16990ea6908bb6abfb07983a | |
| parent | a35ba2f74df5481cb4db1e9d582c708efeb9880d (diff) | |
| download | linux-7ce98a5591d292c7630e2c6804ba0818a75a0f86.tar.bz2 | |
i2c: rcar: explain the lockless design
To make sure people can understand the lockless design of this driver
without the need to dive into git history, add a comment giving an
overview of the situation.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
| -rw-r--r-- | drivers/i2c/busses/i2c-rcar.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/drivers/i2c/busses/i2c-rcar.c b/drivers/i2c/busses/i2c-rcar.c index ce59e14e34b0..a7578f6da979 100644 --- a/drivers/i2c/busses/i2c-rcar.c +++ b/drivers/i2c/busses/i2c-rcar.c @@ -611,6 +611,15 @@ static bool rcar_i2c_slave_irq(struct rcar_i2c_priv *priv) return true; } +/* + * This driver has a lock-free design because there are IP cores (at least + * R-Car Gen2) which have an inherent race condition in their hardware design. + * There, we need to clear RCAR_BUS_MASK_DATA bits as soon as possible after + * the interrupt was generated, otherwise an unwanted repeated message gets + * generated. It turned out that taking a spinlock at the beginning of the ISR + * was already causing repeated messages. Thus, this driver was converted to + * the now lockless behaviour. Please keep this in mind when hacking the driver. + */ static irqreturn_t rcar_i2c_irq(int irq, void *ptr) { struct rcar_i2c_priv *priv = ptr; |