| Message ID | 20190303150314.6528-3-wsa+renesas@sang-engineering.com |
|---|---|
| State | Accepted |
| Headers | show |
| Series | i2c: rcar: improve concurrency | expand |
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@sang-engineering.com> Reviewed-by: Simon Horman <horms+renesas@verge.net.au> > --- > 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 >
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@sang-engineering.com> Applied to for-current, thanks!
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;
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> --- drivers/i2c/busses/i2c-rcar.c | 9 +++++++++ 1 file changed, 9 insertions(+)