linux-kernel - [PATCH 3.14 128/158] usb: phy: am335x-control: wait 1ms after power-up transitions

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Date:	Sun,  4 May 2014 11:40:37 -0400
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Daniel Mack <zonque@...il.com>,
	Felipe Balbi <balbi@...com>
Subject: [PATCH 3.14 128/158] usb: phy: am335x-control: wait 1ms after power-up transitions

3.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Mack <zonque@...il.com>

commit a31a942a148e0083ce560ffeb54fb60e06ab7201 upstream.

Tests have shown that when a power-up transition is followed by other
PHY operations too quickly, the USB port appears dead. Waiting 1ms fixes
this problem.

Signed-off-by: Daniel Mack <zonque@...il.com>
Signed-off-by: Felipe Balbi <balbi@...com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/usb/phy/phy-am335x-control.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/drivers/usb/phy/phy-am335x-control.c
+++ b/drivers/usb/phy/phy-am335x-control.c
@@ -3,6 +3,7 @@
 #include <linux/err.h>
 #include <linux/of.h>
 #include <linux/io.h>
+#include <linux/delay.h>
 #include "am35x-phy-control.h"
 
 struct am335x_control_usb {
@@ -86,6 +87,14 @@ static void am335x_phy_power(struct phy_
 	}
 
 	writel(val, usb_ctrl->phy_reg + reg);
+
+	/*
+	 * Give the PHY ~1ms to complete the power up operation.
+	 * Tests have shown unstable behaviour if other USB PHY related
+	 * registers are written too shortly after such a transition.
+	 */
+	if (on)
+		mdelay(1);
 }
 
 static const struct phy_control ctrl_am335x = {


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