[PATCH v3 3/6] i2c: at91: Send bus clear command if SDA is down

[Codrin Ciubotariu]

After a transfer timeout, some faulty I2C slave devices might hold down
the SDA pin. We can generate a bus clear command, hoping that the slave
might release the pins.
If the CLEAR command is not supported, we will use gpio recovery, if
available, to reset the bus.

Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@xxxxxxxxxxxxx>
---

Changes in v3:
 - rebased on top of i2c/for-next;
  - remove unnecessary initializations with false;
 - replaced SCL with SDA in title and commit message;
 - updated commit message;

Changes in v2:
 - use CLEAR command only if SDA is down; update patch subject to
   reflect this;
 - CLEAR command is no longer used for sama5d2, only sam9x60;

 drivers/i2c/busses/i2c-at91-core.c   |  2 ++
 drivers/i2c/busses/i2c-at91-master.c | 32 +++++++++++++++++++++++-----
 drivers/i2c/busses/i2c-at91.h        |  7 +++++-
 3 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/drivers/i2c/busses/i2c-at91-core.c b/drivers/i2c/busses/i2c-at91-core.c
index 3da1a8acecb5..e14edd236108 100644
--- a/drivers/i2c/busses/i2c-at91-core.c
+++ b/drivers/i2c/busses/i2c-at91-core.c
@@ -131,6 +131,7 @@ static struct at91_twi_pdata sama5d2_config = {
 	.has_dig_filtr = true,
 	.has_adv_dig_filtr = true,
 	.has_ana_filtr = true,
+	.has_clear_cmd = false,	/* due to errata, CLEAR cmd is not working */
 };
 
 static struct at91_twi_pdata sam9x60_config = {
@@ -142,6 +143,7 @@ static struct at91_twi_pdata sam9x60_config = {
 	.has_dig_filtr = true,
 	.has_adv_dig_filtr = true,
 	.has_ana_filtr = true,
+	.has_clear_cmd = true,
 };
 
 static const struct of_device_id atmel_twi_dt_ids[] = {
diff --git a/drivers/i2c/busses/i2c-at91-master.c b/drivers/i2c/busses/i2c-at91-master.c
index 0aba51a7df32..bcc05a8fe826 100644
--- a/drivers/i2c/busses/i2c-at91-master.c
+++ b/drivers/i2c/busses/i2c-at91-master.c
@@ -480,7 +480,7 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
 	unsigned long time_left;
 	bool has_unre_flag = dev->pdata->has_unre_flag;
 	bool has_alt_cmd = dev->pdata->has_alt_cmd;
-	struct i2c_bus_recovery_info *rinfo = &dev->rinfo;
+	bool has_clear_cmd = dev->pdata->has_clear_cmd;
 
 	/*
 	 * WARNING: the TXCOMP bit in the Status Register is NOT a clear on
@@ -641,10 +641,32 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
 			       AT91_TWI_THRCLR | AT91_TWI_LOCKCLR);
 	}
 
-	if (rinfo->get_sda && !(rinfo->get_sda(&dev->adapter))) {
-		dev_dbg(dev->dev,
-			"SDA is down; clear bus using gpio\n");
-		i2c_recover_bus(&dev->adapter);
+	/*
+	 * some faulty I2C slave devices might hold SDA down;
+	 * we can send a bus clear command, hoping that the pins will be
+	 * released
+	 */
+	if (has_clear_cmd) {
+		if (!(dev->transfer_status & AT91_TWI_SDA)) {
+			dev_dbg(dev->dev,
+				"SDA is 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);
+		}
+	} else {
+		struct i2c_bus_recovery_info *rinfo = &dev->rinfo;
+
+		if (rinfo->get_sda && !(rinfo->get_sda(&dev->adapter))) {
+			dev_dbg(dev->dev,
+				"SDA is down; clear bus using gpio\n");
+			i2c_recover_bus(&dev->adapter);
+		}
 	}
 
 	return ret;
diff --git a/drivers/i2c/busses/i2c-at91.h b/drivers/i2c/busses/i2c-at91.h
index f57a6cab96b4..7e7b4955ca7f 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_FILTR		0x0044
@@ -118,6 +122,7 @@ struct at91_twi_pdata {
 	bool has_dig_filtr;
 	bool has_adv_dig_filtr;
 	bool has_ana_filtr;
+	bool has_clear_cmd;
 	struct at_dma_slave dma_slave;
 };
 
-- 
2.20.1