On Sun, Mar 03, 2019 at 04:03:14PM +0100, Wolfram Sang wrote:
> 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@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Simon Horman <horms+renesas@xxxxxxxxxxxx>
> ---
> drivers/i2c/busses/i2c-rcar.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/drivers/i2c/busses/i2c-rcar.c b/drivers/i2c/busses/i2c-rcar.c
> index 6410896f717b..3ce74edcd70c 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;
> --
> 2.11.0
>
