[PATCH AUTOSEL 4.14 4/6] i2c: rk3x: Handle a spurious start completion interrupt flag

[Sasha Levin]

From: Ondrej Jirman <megous at megous.com>

[ Upstream commit 02fe0fbd8a21e183687925c3a266ae27dda9840f ]

In a typical read transfer, start completion flag is being set after
read finishes (notice ipd bit 4 being set):

trasnfer poll=0
i2c start
rk3x-i2c fdd40000.i2c: IRQ: state 1, ipd: 10
i2c read
rk3x-i2c fdd40000.i2c: IRQ: state 2, ipd: 1b
i2c stop
rk3x-i2c fdd40000.i2c: IRQ: state 4, ipd: 33

This causes I2C transfer being aborted in polled mode from a stop completion
handler:

trasnfer poll=1
i2c start
rk3x-i2c fdd40000.i2c: IRQ: state 1, ipd: 10
i2c read
rk3x-i2c fdd40000.i2c: IRQ: state 2, ipd: 0
rk3x-i2c fdd40000.i2c: IRQ: state 2, ipd: 1b
i2c stop
rk3x-i2c fdd40000.i2c: IRQ: state 4, ipd: 13
i2c stop
rk3x-i2c fdd40000.i2c: unexpected irq in STOP: 0x10

Clearing the START flag after read fixes the issue without any obvious
side effects.

This issue was dicovered on RK3566 when adding support for powering
off the RK817 PMIC.

Signed-off-by: Ondrej Jirman <megous at megous.com>
Reviewed-by: John Keeping <john at metanate.com>
Signed-off-by: Wolfram Sang <wsa at kernel.org>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 drivers/i2c/busses/i2c-rk3x.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-rk3x.c b/drivers/i2c/busses/i2c-rk3x.c
index fe234578380ac..548089aa9aba5 100644
--- a/drivers/i2c/busses/i2c-rk3x.c
+++ b/drivers/i2c/busses/i2c-rk3x.c
@@ -424,8 +424,8 @@ static void rk3x_i2c_handle_read(struct rk3x_i2c *i2c, unsigned int ipd)
 	if (!(ipd & REG_INT_MBRF))
 		return;
 
-	/* ack interrupt */
-	i2c_writel(i2c, REG_INT_MBRF, REG_IPD);
+	/* ack interrupt (read also produces a spurious START flag, clear it too) */
+	i2c_writel(i2c, REG_INT_MBRF | REG_INT_START, REG_IPD);
 
 	/* Can only handle a maximum of 32 bytes at a time */
 	if (len > 32)
-- 
2.33.0