pi2usb9281: Prevent race condition in RMW control register

Added unlocked versions of register access,
modified RMW functions to use unlocked versions
and made them locked themselves.

BRANCH=master
BUG=chrome-os-partner:49182
TEST=DUT boots successfully

Change-Id: Ifd16abc349cc731aeed78b12989595214e65cea2
Signed-off-by: Victor Prupis <vprupis@google.com>
Reviewed-on: https://chromium-review.googlesource.com/377151
Commit-Ready: Shawn N <shawnn@chromium.org>
Reviewed-by: Shawn N <shawnn@chromium.org>

1 files changed, 69 insertions, 25 deletions

diff --git a/driver/usb_switch_pi3usb9281.c b/driver/usb_switch_pi3usb9281.c
index e97a04f8db..39b037cf49 100644
--- a/driver/usb_switch_pi3usb9281.c
+++ b/driver/usb_switch_pi3usb9281.c
@@ -61,14 +61,18 @@ static void unselect_chip(int port)
 		mutex_unlock(chip->mux_lock);
 }
 
-static uint8_t pi3usb9281_read(int port, uint8_t reg)
+static uint8_t pi3usb9281_do_read(int port, uint8_t reg, int with_lock)
 {
 	struct pi3usb9281_config *chip = &pi3usb9281_chips[port];
 	int res, val;
 
-	select_chip(port);
+	if (with_lock)
+		select_chip(port);
+
 	res = i2c_read8(chip->i2c_port, PI3USB9281_I2C_ADDR, reg, &val);
-	unselect_chip(port);
+
+	if (with_lock)
+		unselect_chip(port);
 
 	if (res)
 		return 0xee;
@@ -76,26 +80,56 @@ static uint8_t pi3usb9281_read(int port, uint8_t reg)
 	return val;
 }
 
-static int pi3usb9281_write(int port, uint8_t reg, uint8_t val)
+static uint8_t pi3usb9281_read_u(int port, uint8_t reg)
+{
+	return pi3usb9281_do_read(port, reg, 0);
+}
+
+static uint8_t pi3usb9281_read(int port, uint8_t reg)
+{
+	return pi3usb9281_do_read(port, reg, 1);
+}
+
+static int pi3usb9281_do_write(
+	int port, uint8_t reg, uint8_t val, int with_lock)
 {
 	struct pi3usb9281_config *chip = &pi3usb9281_chips[port];
 	int res;
 
-	select_chip(port);
+	if (with_lock)
+		select_chip(port);
+
 	res = i2c_write8(chip->i2c_port, PI3USB9281_I2C_ADDR, reg, val);
-	unselect_chip(port);
+
+	if (with_lock)
+		unselect_chip(port);
 
 	if (res)
 		CPRINTS("PI3USB9281 I2C write failed");
 	return res;
 }
 
+static int pi3usb9281_write(int port, uint8_t reg, uint8_t val)
+{
+	return pi3usb9281_do_write(port, reg, val, 1);
+}
+
 /* Write control register, taking care to correctly set reserved bits. */
-static int pi3usb9281_write_ctrl(int port, uint8_t ctrl)
+static int pi3usb9281_do_write_ctrl(int port, uint8_t ctrl, int with_lock)
 {
-	return pi3usb9281_write(port, PI3USB9281_REG_CONTROL,
+	return pi3usb9281_do_write(port, PI3USB9281_REG_CONTROL,
 				(ctrl & PI3USB9281_CTRL_MASK) |
-				PI3USB9281_CTRL_RSVD_1);
+				PI3USB9281_CTRL_RSVD_1, with_lock);
+}
+
+static int pi3usb9281_write_ctrl(int port, uint8_t ctrl)
+{
+	return pi3usb9281_do_write_ctrl(port, ctrl, 1);
+}
+
+static int pi3usb9281_write_ctrl_u(int port, uint8_t ctrl)
+{
+	return pi3usb9281_do_write_ctrl(port, ctrl, 0);
 }
 
 static int pi3usb9281_set_interrupt_mask(int port, uint8_t mask)
@@ -190,17 +224,22 @@ static int pi3usb9281_reset(int port)
 
 static int pi3usb9281_set_switch_manual(int port, int val)
 {
-	uint8_t ctrl = pi3usb9281_read(port, PI3USB9281_REG_CONTROL);
+	int res = EC_ERROR_UNKNOWN;
+	uint8_t ctrl;
 
-	if (ctrl == 0xee)
-		return EC_ERROR_UNKNOWN;
+	select_chip(port);
+	ctrl = pi3usb9281_read_u(port, PI3USB9281_REG_CONTROL);
 
-	if (val)
-		ctrl &= ~PI3USB9281_CTRL_AUTO;
-	else
-		ctrl |= PI3USB9281_CTRL_AUTO;
+	if (ctrl != 0xee) {
+		if (val)
+			ctrl &= ~PI3USB9281_CTRL_AUTO;
+		else
+			ctrl |= PI3USB9281_CTRL_AUTO;
+		res = pi3usb9281_write_ctrl_u(port, ctrl);
+	}
 
-	return pi3usb9281_write_ctrl(port, ctrl);
+	unselect_chip(port);
+	return res;
 }
 
 static int pi3usb9281_set_pins(int port, uint8_t val)
@@ -210,17 +249,22 @@ static int pi3usb9281_set_pins(int port, uint8_t val)
 
 static int pi3usb9281_set_switches(int port, int open)
 {
-	uint8_t ctrl = pi3usb9281_read(port, PI3USB9281_REG_CONTROL);
+	int res = EC_ERROR_UNKNOWN;
+	uint8_t ctrl;
 
-	if (ctrl == 0xee)
-		return EC_ERROR_UNKNOWN;
+	select_chip(port);
+	ctrl = pi3usb9281_read_u(port, PI3USB9281_REG_CONTROL);
 
-	if (open)
-		ctrl &= ~PI3USB9281_CTRL_SWITCH_AUTO;
-	else
-		ctrl |= PI3USB9281_CTRL_SWITCH_AUTO;
+	if (ctrl != 0xee) {
+		if (open)
+			ctrl &= ~PI3USB9281_CTRL_SWITCH_AUTO;
+		else
+			ctrl |= PI3USB9281_CTRL_SWITCH_AUTO;
+		res = pi3usb9281_write_ctrl_u(port, ctrl);
+	}
 
-	return pi3usb9281_write_ctrl(port, ctrl);
+	unselect_chip(port);
+	return res;
 }
 
 void usb_charger_set_switches(int port, enum usb_switch setting)