[PATCH] usb: usb251xb: check if hub is already attached

[Marco Felsch <m.felsch@pengutronix.de>]

It is possible that the hub was configured earlier by the bootloader and
we lack of the reset-gpio. In such a case the usb251xb_connect() fails
because the registers are write-protected. Add a check to test if the
hub is already connected and don't try to reconfigure the hub if we
can't toggle the reset pin. Don't change the usb251xb_connect() logic
if we can't read the status.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
---
 drivers/usb/misc/usb251xb.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/drivers/usb/misc/usb251xb.c b/drivers/usb/misc/usb251xb.c
index 29fe5771c21b..9f9a64bab059 100644
--- a/drivers/usb/misc/usb251xb.c
+++ b/drivers/usb/misc/usb251xb.c
@@ -266,6 +266,30 @@ static int usb251x_check_gpio_chip(struct usb251xb *hub)
 }
 #endif
 
+static bool usb251xb_hub_attached(struct usb251xb *hub)
+{
+	char i2c_rb;
+	int err;
+
+	err = i2c_smbus_read_block_data(hub->i2c, USB251XB_ADDR_STATUS_COMMAND,
+					&i2c_rb);
+	if (err < 0) {
+		/*
+		 * The device disables the i2c-interface immediately after it
+		 * received the USB_ATTACH signal.
+		 */
+		if (err == -ENXIO)
+			return true;
+
+		dev_warn(hub->dev,
+			 "Checking hub Status/Command register failed: %d\n",
+			 err);
+		return false;
+	}
+
+	return !!(i2c_rb & USB251XB_STATUS_COMMAND_ATTACH);
+}
+
 static void usb251xb_reset(struct usb251xb *hub)
 {
 	if (!hub->gpio_reset)
@@ -288,6 +312,15 @@ static int usb251xb_connect(struct usb251xb *hub)
 	struct device *dev = hub->dev;
 	int err, i;
 	char i2c_wb[USB251XB_I2C_REG_SZ];
+	bool is_attached;
+
+	/*
+	 * Check if configuration was done earlier by the bootloader. Trust them
+	 * if it is the case and we are not capable to reset the hub.
+	 */
+	is_attached = usb251xb_hub_attached(hub);
+	if (!hub->gpio_reset && is_attached)
+		return 0;
 
 	memset(i2c_wb, 0, USB251XB_I2C_REG_SZ);
 
-- 
2.20.1