[PATCH v3] i2c: at91: support atomic write xfer

[MichaÅ MirosÅaw]

Implement basic support for atomic write - enough to get a simple
write to PMIC on shutdown. Only for chips having ALT_CMD register,
eg. SAMA5D2.

Signed-off-by: MichaÅ MirosÅaw <mirq-linux@xxxxxxxxxxxx>
---
v2: remove runtime-PM usage
    switch to readl*poll*atomic() for transfer completion wait
v3: build fixes
---
 drivers/i2c/busses/i2c-at91-master.c | 69 +++++++++++++++++++++++++++-
 1 file changed, 67 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-at91-master.c b/drivers/i2c/busses/i2c-at91-master.c
index ba6fbb9c7390..10c66809df83 100644
--- a/drivers/i2c/busses/i2c-at91-master.c
+++ b/drivers/i2c/busses/i2c-at91-master.c
@@ -21,8 +21,10 @@
 #include <linux/i2c.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
+#include <linux/pinctrl/consumer.h>
 #include <linux/platform_device.h>
 #include <linux/platform_data/dma-atmel.h>
 #include <linux/pm_runtime.h>
@@ -709,6 +711,68 @@ static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
 	return ret;
 }
 
+static int at91_twi_xfer_atomic(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
+{
+	struct at91_twi_dev *dev = i2c_get_adapdata(adap);
+	struct pinctrl *pins;
+	__u32 stat;
+	int ret;
+
+	/* FIXME: only single write request supported to 7-bit addr */
+	if (num != 1)
+		return -EOPNOTSUPP;
+	if (msg->flags & I2C_M_RD)
+		return -EOPNOTSUPP;
+	if (msg->flags & I2C_M_TEN)
+		return -EOPNOTSUPP;
+	if (msg->len > dev->fifo_size && msg->len > 1)
+		return -EOPNOTSUPP;
+	if (!dev->pdata->has_alt_cmd)
+		return -EOPNOTSUPP;
+
+	pins = pinctrl_get_select_default(&adap->dev);
+
+	ret = clk_prepare_enable(dev->clk);
+	if (ret)
+		goto out;
+
+	/* Clear and disable pending interrupts, such as NACK. */
+	at91_twi_read(dev, AT91_TWI_SR);
+	at91_twi_write(dev, AT91_TWI_IDR, ~0);
+
+	at91_twi_write(dev, AT91_TWI_MMR, msg->addr << 16);
+
+	if (!msg->len) {
+		at91_twi_write(dev, AT91_TWI_CR,
+			       AT91_TWI_ACMDIS | AT91_TWI_QUICK);
+	} else {
+		size_t n = msg->len;
+		__u8 *p;
+
+		at91_twi_write(dev, AT91_TWI_CR,
+				    AT91_TWI_ACMEN |
+				    AT91_TWI_THRCLR | AT91_TWI_RHRCLR);
+		at91_twi_write(dev, AT91_TWI_ACR, AT91_TWI_ACR_DATAL(n));
+		for (p = msg->buf; n--; ++p)
+			writeb_relaxed(*p, dev->base + AT91_TWI_THR);
+	}
+
+	readl_relaxed_poll_timeout_atomic(dev->base + AT91_TWI_SR, stat,
+					  stat & AT91_TWI_TXCOMP, 100,
+					  (2 + msg->len) * 1000);
+	if (stat & AT91_TWI_NACK)
+		ret = -EREMOTEIO;
+	else
+		ret = num;
+
+	clk_disable_unprepare(dev->clk);
+out:
+	if (!IS_ERR(pins))
+		pinctrl_put(pins);
+
+	return ret;
+}
+
 /*
  * The hardware can handle at most two messages concatenated by a
  * repeated start via it's internal address feature.
@@ -725,8 +789,9 @@ static u32 at91_twi_func(struct i2c_adapter *adapter)
 }
 
 static const struct i2c_algorithm at91_twi_algorithm = {
-	.master_xfer	= at91_twi_xfer,
-	.functionality	= at91_twi_func,
+	.master_xfer		= at91_twi_xfer,
+	.master_xfer_atomic	= at91_twi_xfer_atomic,
+	.functionality		= at91_twi_func,
 };
 
 static int at91_twi_configure_dma(struct at91_twi_dev *dev, u32 phy_addr)
-- 
2.20.1