linux-kernel - [PATCH] usb: misc: usb3503: make sure reset is low for at least 100us

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Date:   Thu, 11 Jan 2018 14:47:40 +0100
From:   Stefan Agner <stefan@...er.ch>
To:     gregkh@...uxfoundation.org
Cc:     felipe.balbi@...ux.intel.com, johan@...nel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Stefan Agner <stefan@...er.ch>
Subject: [PATCH] usb: misc: usb3503: make sure reset is low for at least 100us

When using a GPIO which is high by default, and initialize the
driver in USB Hub mode, initialization fails with:
  [  111.757794] usb3503 0-0008: SP_ILOCK failed (-5)

The reason seems to be that the chip is not properly reset.
Probe does initialize reset low, however some lines later the
code already set it back high, which is not long enouth.

Make sure reset is asserted for at least 100us by inserting a
delay after initializing the reset pin during probe.

Signed-off-by: Stefan Agner <stefan@...er.ch>
---
 drivers/usb/misc/usb3503.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/usb/misc/usb3503.c b/drivers/usb/misc/usb3503.c
index 465dbf68b463..f723f7b8c9ac 100644
--- a/drivers/usb/misc/usb3503.c
+++ b/drivers/usb/misc/usb3503.c
@@ -279,6 +279,8 @@ static int usb3503_probe(struct usb3503 *hub)
 	if (gpio_is_valid(hub->gpio_reset)) {
 		err = devm_gpio_request_one(dev, hub->gpio_reset,
 				GPIOF_OUT_INIT_LOW, "usb3503 reset");
+		/* Datasheet defines a hardware reset to be at least 100us */
+		usleep_range(100, 10000);
 		if (err) {
 			dev_err(dev,
 				"unable to request GPIO %d as reset pin (%d)\n",
-- 
2.15.1