linux-kernel - [PATCH V2] i2c-designware: Mask all interrupts during i2c controller enable

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Date:	Thu, 10 Apr 2014 23:03:19 +0000
From:	"Du, Wenkai" <wenkai.du@...el.com>
To:	"'linux-i2c@...r.kernel.org'" <linux-i2c@...r.kernel.org>
CC:	'Wolfram Sang' <wsa@...-dreams.de>,
	"Westerberg, Mika" <mika.westerberg@...el.com>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>
Subject: [PATCH V2] i2c-designware: Mask all interrupts during i2c
 controller enable

Hi all,

Updated problem descriptions from Mika's feedback and new test data: 

There have been "i2c_designware 80860F41:00: controller timed out" errors
on a number of Baytrail platforms. The issue is caused by incorrect value in
Interrupt Mask Register (DW_IC_INTR_MASK)  when i2c core is being enabled. 
This causes call to __i2c_dw_enable() to immediately start the transfer which
leads to timeout. There are 3 failure modes observed:

1. Failure in S0 to S3 resume path

The default value after reset for DW_IC_INTR_MASK is 0x8ff. When we start 
the first transaction after resuming from system sleep, TX_EMPTY interrupt 
is already unmasked because of the hardware default.

2. Failure in normal operational path

This failure happens rarely and is hard to reproduce. Debug trace showed that
DW_IC_INTR_MASK had value of 0x254 when failure occurred, which meant 
TX_EMPTY was unmasked.

2. Failure in S3 to S0 suspend path

This failure also happens rarely and is hard to reproduce. Adding debug trace
that read DW_IC_INTR_MASK made this failure not reproducible. But from ISR 
call trace we could conclude TX_EMPTY was unmasked when problem occurred.

The patch masks all interrupts before the controller is enabled to resolve the
faulty DW_IC_INTR_MASK conditions.

Signed-off-by: Wenkai Du <wenkai.du@...el.com>
---
 drivers/i2c/busses/i2c-designware-core.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
index 14c4b30..71a3fa9 100644
--- a/drivers/i2c/busses/i2c-designware-core.c
+++ b/drivers/i2c/busses/i2c-designware-core.c
@@ -417,6 +417,9 @@ static void i2c_dw_xfer_init(struct dw_i2c_dev *dev)
 	 */
 	dw_writel(dev, msgs[dev->msg_write_idx].addr | ic_tar, DW_IC_TAR);

+	/* disable interrupts */
+	i2c_dw_disable_int(dev);
+
 	/* Enable the adapter */
 	__i2c_dw_enable(dev, true);

-- 
1.7.9.5

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