[PATCH v2 3/6] i2c: at91: Send bus clear command if SCL is down

Codrin.Ciubotariu
2020-01-03T09:49:32Z

After a transfer timeout, some faulty I2C slave devices might hold down
the SCL pin. We can generate a bus clear command, hoping that the slave
might release the pins.

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

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 | 9 ++++++++
drivers/i2c/busses/i2c-at91-master.c | 32 +++++++++++++++++++++++-----
drivers/i2c/busses/i2c-at91.h | 7 +++++-
3 files changed, 42 insertions(+), 6 deletions(-)

diff --git a/drivers/i2c/busses/i2c-at91-core.c b/drivers/i2c/busses/i2c-at91-core.c
index e13af4874976..128eafc05adb 100644
--- a/drivers/i2c/busses/i2c-at91-core.c
+++ b/drivers/i2c/busses/i2c-at91-core.c
@@ -71,6 +71,7 @@ static struct at91_twi_pdata at91rm9200_config = {
.has_dig_filtr = false,
.has_adv_dig_filtr = false,
.has_ana_filtr = false,
+ .has_clear_cmd = false,
};

static struct at91_twi_pdata at91sam9261_config = {
@@ -82,6 +83,7 @@ static struct at91_twi_pdata at91sam9261_config = {
.has_dig_filtr = false,
.has_adv_dig_filtr = false,
.has_ana_filtr = false,
+ .has_clear_cmd = false,
};

static struct at91_twi_pdata at91sam9260_config = {
@@ -93,6 +95,7 @@ static struct at91_twi_pdata at91sam9260_config = {
.has_dig_filtr = false,
.has_adv_dig_filtr = false,
.has_ana_filtr = false,
+ .has_clear_cmd = false,
};

static struct at91_twi_pdata at91sam9g20_config = {
@@ -104,6 +107,7 @@ static struct at91_twi_pdata at91sam9g20_config = {
.has_dig_filtr = false,
.has_adv_dig_filtr = false,
.has_ana_filtr = false,
+ .has_clear_cmd = false,
};

static struct at91_twi_pdata at91sam9g10_config = {
@@ -115,6 +119,7 @@ static struct at91_twi_pdata at91sam9g10_config = {
.has_dig_filtr = false,
.has_adv_dig_filtr = false,
.has_ana_filtr = false,
+ .has_clear_cmd = false,
};

static const struct platform_device_id at91_twi_devtypes[] = {
@@ -148,6 +153,7 @@ static struct at91_twi_pdata at91sam9x5_config = {
.has_dig_filtr = false,
.has_adv_dig_filtr = false,
.has_ana_filtr = false,
+ .has_clear_cmd = false,
};

static struct at91_twi_pdata sama5d4_config = {
@@ -159,6 +165,7 @@ static struct at91_twi_pdata sama5d4_config = {
.has_dig_filtr = true,
.has_adv_dig_filtr = false,
.has_ana_filtr = false,
+ .has_clear_cmd = false,
};

static struct at91_twi_pdata sama5d2_config = {
@@ -170,6 +177,7 @@ 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 = {
@@ -181,6 +189,7 @@ 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 c55e8ff35201..8c4f20317847 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 eb335b71e775..80f77d523346 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