summaryrefslogtreecommitdiff
path: root/drivers/i2c
diff options
context:
space:
mode:
authorWolfram Sang <wsa+renesas@sang-engineering.com>2019-03-03 18:03:14 +0300
committerWolfram Sang <wsa@the-dreams.de>2019-03-12 16:09:33 +0300
commit7ce98a5591d292c7630e2c6804ba0818a75a0f86 (patch)
tree94d005b4d29d247b16990ea6908bb6abfb07983a /drivers/i2c
parenta35ba2f74df5481cb4db1e9d582c708efeb9880d (diff)
downloadlinux-7ce98a5591d292c7630e2c6804ba0818a75a0f86.tar.xz
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>
Diffstat (limited to 'drivers/i2c')
-rw-r--r--drivers/i2c/busses/i2c-rcar.c9
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;