[PATCH 3/3] misc: atsha204a: fix wakeup function

["Michał Barnaś" <barnas@google.com>]

The ATSHA204A chip requires SDA line to go low for at least 60us to
wake up the chip. Previous implementation did not meet this requirement
due to the NAK received on bus and not sending the zeroes.
The function to ignore the NAK and send bytes regardless is not
supported in the u-boot making it impossible to wake up the chip
this way.
Instead, the bus speed, if needed, is set to lowest value and the
message is sent to the address 0x0. This way, the address of zero
makes the SDA line go low for about 80us, meeting the required time
to wake up the chip. The zero length packet is not sent by the i2c,
so the one byte is sent to the transfer function, but only the address
is sent anyway.
After sending the zero address, the bus speed is restored to the
previous value if it was slowed down to wake up the chip.

Signed-off-by: Michał Barnaś <barnas@google.com>
---

 drivers/misc/atsha204a-i2c.c | 49 ++++++++++++++++++++++++++++++++----
 1 file changed, 44 insertions(+), 5 deletions(-)

diff --git a/drivers/misc/atsha204a-i2c.c b/drivers/misc/atsha204a-i2c.c
index 29daefb2a5..707daa90bd 100644
--- a/drivers/misc/atsha204a-i2c.c
+++ b/drivers/misc/atsha204a-i2c.c
@@ -21,7 +21,6 @@
 #include <linux/bitrev.h>
 #include <u-boot/crc.h>
 
-#define ATSHA204A_TWLO_US		60
 #define ATSHA204A_TWHI_US		2500
 #define ATSHA204A_TRANSACTION_TIMEOUT	100000
 #define ATSHA204A_TRANSACTION_RETRY	5
@@ -34,6 +33,48 @@ static inline u16 atsha204a_crc16(const u8 *buffer, size_t len)
 	return bitrev16(crc16(0, buffer, len));
 }
 
+static int atsha204a_ping_bus(struct udevice *dev)
+{
+	struct udevice *bus = dev_get_parent(dev);
+	struct i2c_msg msg;
+	int speed;
+	int res;
+	u8 val = 0;
+
+	speed = dm_i2c_get_bus_speed(bus);
+	if (speed != I2C_SPEED_STANDARD_RATE) {
+		int rv;
+
+		rv = dm_i2c_set_bus_speed(bus, I2C_SPEED_STANDARD_RATE);
+		if (rv)
+			debug("Couldn't change the I2C bus speed\n");
+	}
+
+	/*
+	 * The I2C drivers don't support sending messages when NAK is received.
+	 * This chip requires wake up low signal on SDA for >= 60us.
+	 * To achieve this, we slow the bus to 100kHz and send an empty
+	 * message to address 0. This will hold the SDA line low for the
+	 * required time to wake up the chip.
+	 */
+	msg.addr = 0;
+	msg.flags = I2C_M_STOP;
+	msg.len = sizeof(val);
+	msg.buf = &val;
+
+	res = dm_i2c_xfer(dev, &msg, 1);
+
+	if (speed != I2C_SPEED_STANDARD_RATE) {
+		int rv;
+
+		rv = dm_i2c_set_bus_speed(bus, speed);
+		if (rv)
+			debug("Couldn't restore the I2C bus speed\n");
+	}
+
+	return res;
+}
+
 static int atsha204a_send(struct udevice *dev, const u8 *buf, u8 len)
 {
 	fdt_addr_t *priv = dev_get_priv(dev);
@@ -94,7 +135,6 @@ static int atsha204a_recv_resp(struct udevice *dev,
 
 int atsha204a_wakeup(struct udevice *dev)
 {
-	u8 req[4];
 	struct atsha204a_resp resp;
 	int res;
 
@@ -105,10 +145,9 @@ int atsha204a_wakeup(struct udevice *dev)
 	 * when the device is idle, asleep or during waking up.
 	 * Don't check for error when waking up the device.
 	 */
-	memset(req, 0, 4);
-	atsha204a_send(dev, req, 4);
+	atsha204a_ping_bus(dev);
 
-	udelay(ATSHA204A_TWLO_US + ATSHA204A_TWHI_US);
+	udelay(ATSHA204A_TWHI_US);
 
 	res = atsha204a_recv_resp(dev, &resp);
 	if (res) {
-- 
2.44.0.rc0.258.g7320e95886-goog