linux-kernel - [PATCH v1] i2c: npcm7xx: Clear LAST bit after a failed transaction.

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Message-Id: <20200920204809.132911-1-tali.perry1@gmail.com>
Date:   Sun, 20 Sep 2020 23:48:09 +0300
From:   Tali Perry <tali.perry1@...il.com>
To:     wsa@...nel.org, andriy.shevchenko@...ux.intel.com,
        kunyi@...gle.com, benjaminfair@...gle.com, avifishman70@...il.com,
        joel@....id.au, tmaimon77@...il.com
Cc:     linux-i2c@...r.kernel.org, openbmc@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, Tali Perry <tali.perry1@...il.com>
Subject: [PATCH v1] i2c: npcm7xx: Clear LAST bit after a failed transaction.

Due to a HW issue, in some scenarios the LAST bit might remain set.
This will cause an unexpected NACK after reading 16 bytes on the next
read.

Example: if user tries to read from a missing device, get a NACK,
then if the next command is a long read ( > 16 bytes),
the master will stop reading after 16 bytes.
To solve this, if a command fails, check if LAST bit is still
set. If it does, reset the module.

Fixes: 56a1485b102e (i2c: npcm7xx: Add Nuvoton NPCM I2C controller driver)
Signed-off-by: Tali Perry <tali.perry1@...il.com>
---
 drivers/i2c/busses/i2c-npcm7xx.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/i2c/busses/i2c-npcm7xx.c b/drivers/i2c/busses/i2c-npcm7xx.c
index dfcf04e1967f..2ad166355ec9 100644
--- a/drivers/i2c/busses/i2c-npcm7xx.c
+++ b/drivers/i2c/busses/i2c-npcm7xx.c
@@ -2163,6 +2163,15 @@ static int npcm_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
 	if (bus->cmd_err == -EAGAIN)
 		ret = i2c_recover_bus(adap);
 
+	/*
+	 * After any type of error, check if LAST bit is still set,
+	 * due to a HW issue.
+	 * It cannot be cleared without resetting the module.
+	 */
+	if (bus->cmd_err &&
+	    (NPCM_I2CRXF_CTL_LAST_PEC & ioread8(bus->reg + NPCM_I2CRXF_CTL)))
+		npcm_i2c_reset(bus);
+
 #if IS_ENABLED(CONFIG_I2C_SLAVE)
 	/* reenable slave if it was enabled */
 	if (bus->slave)

base-commit: 856deb866d16e29bd65952e0289066f6078af773
-- 
2.22.0