From 7ce98a5591d292c7630e2c6804ba0818a75a0f86 Mon Sep 17 00:00:00 2001 From: Wolfram Sang Date: Sun, 3 Mar 2019 16:03:14 +0100 Subject: 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 Reviewed-by: Simon Horman Signed-off-by: Wolfram Sang --- drivers/i2c/busses/i2c-rcar.c | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'drivers/i2c') 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; -- cgit