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i2c: rcar: explain the lockless design

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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>
This commit is contained in:
Wolfram Sang 2019-03-03 16:03:14 +01:00 committed by Wolfram Sang
parent a35ba2f74d
commit 7ce98a5591
1 changed files with 9 additions and 0 deletions
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9
drivers/i2c/busses/i2c-rcar.c
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@ -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;