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Subject[PATCH] i2c: at91: Send bus clear command if SCL or SDA is down
Date
After a transfer timeout, some faulty I2C slave devices might hold down
the SCL or the SDA pins. We can generate a bus clear command, hoping that
the slave might release the pins.

Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
---
drivers/i2c/busses/i2c-at91-master.c | 20 ++++++++++++++++++++
drivers/i2c/busses/i2c-at91.h | 6 +++++-
2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-at91-master.c b/drivers/i2c/busses/i2c-at91-master.c
index a3fcc35ffd3b..5f544a16db96 100644
--- a/drivers/i2c/busses/i2c-at91-master.c
+++ b/drivers/i2c/busses/i2c-at91-master.c
@@ -599,6 +599,26 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
at91_twi_write(dev, AT91_TWI_CR,
AT91_TWI_THRCLR | AT91_TWI_LOCKCLR);
}
+
+ /*
+ * After timeout, some faulty I2C slave devices might hold SCL/SDA down;
+ * we can send a bus clear command, hoping that the pins will be
+ * released
+ */
+ if (!(dev->transfer_status & AT91_TWI_SDA) ||
+ !(dev->transfer_status & AT91_TWI_SCL)) {
+ dev_dbg(dev->dev,
+ "SDA/SCL are down; sending bus clear command\n");
+ if (dev->use_alt_cmd) {
+ unsigned int acr;
+
+ acr = at91_twi_read(dev, AT91_TWI_ACR);
+ acr &= ~AT91_TWI_ACR_DATAL_MASK;
+ at91_twi_write(dev, AT91_TWI_ACR, acr);
+ }
+ at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_CLEAR);
+ }
+
return ret;
}

diff --git a/drivers/i2c/busses/i2c-at91.h b/drivers/i2c/busses/i2c-at91.h
index 499b506f6128..ffb870f3ffc6 100644
--- a/drivers/i2c/busses/i2c-at91.h
+++ b/drivers/i2c/busses/i2c-at91.h
@@ -36,6 +36,7 @@
#define AT91_TWI_SVDIS BIT(5) /* Slave Transfer Disable */
#define AT91_TWI_QUICK BIT(6) /* SMBus quick command */
#define AT91_TWI_SWRST BIT(7) /* Software Reset */
+#define AT91_TWI_CLEAR BIT(15) /* Bus clear command */
#define AT91_TWI_ACMEN BIT(16) /* Alternative Command Mode Enable */
#define AT91_TWI_ACMDIS BIT(17) /* Alternative Command Mode Disable */
#define AT91_TWI_THRCLR BIT(24) /* Transmit Holding Register Clear */
@@ -69,6 +70,8 @@
#define AT91_TWI_NACK BIT(8) /* Not Acknowledged */
#define AT91_TWI_EOSACC BIT(11) /* End Of Slave Access */
#define AT91_TWI_LOCK BIT(23) /* TWI Lock due to Frame Errors */
+#define AT91_TWI_SCL BIT(24) /* TWI SCL status */
+#define AT91_TWI_SDA BIT(25) /* TWI SDA status */

#define AT91_TWI_INT_MASK \
(AT91_TWI_TXCOMP | AT91_TWI_RXRDY | AT91_TWI_TXRDY | AT91_TWI_NACK \
@@ -81,7 +84,8 @@
#define AT91_TWI_THR 0x0034 /* Transmit Holding Register */

#define AT91_TWI_ACR 0x0040 /* Alternative Command Register */
-#define AT91_TWI_ACR_DATAL(len) ((len) & 0xff)
+#define AT91_TWI_ACR_DATAL_MASK GENMASK(15, 0)
+#define AT91_TWI_ACR_DATAL(len) ((len) & AT91_TWI_ACR_DATAL_MASK)
#define AT91_TWI_ACR_DIR BIT(8)

#define AT91_TWI_FMR 0x0050 /* FIFO Mode Register */
--
2.20.1
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