[U-Boot] [PATCH 1/3] ARM: tegra: fix USB ULPI PHY reset signal inversion confusion

[Stephen Warren <swarren@wwwdotorg.org>]

From: Stephen Warren <swarren@nvidia.com>

USB ULPI PHY reset signals are typically active low. Consequently, they
should be marked as GPIO_ACTIVE_LOW in device tree, and indeed they are in
the Linux kernel DTs, and in DT properties that U-Boot doesn't yet use.
However, in DT properties that U-Boot does use, the value has been set to
0 (== GPIO_ACTIVE_HIGH) to work around a bug in U-Boot.

This change fixes the DT to correctly represent the HW, and fixes the
Tegra USB driver to cope with the fact that dm_gpio_set_value() internally
handles any inversions implied by the DT value GPIO_ACTIVE_LOW.

Cc: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
---
 arch/arm/dts/tegra20-colibri.dts |  3 ++-
 arch/arm/dts/tegra20-harmony.dts |  3 ++-
 drivers/usb/host/ehci-tegra.c    | 13 +++++++++++--
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/arm/dts/tegra20-colibri.dts b/arch/arm/dts/tegra20-colibri.dts
index a291d93c7d01..777f63e5bdb6 100644
--- a/arch/arm/dts/tegra20-colibri.dts
+++ b/arch/arm/dts/tegra20-colibri.dts
@@ -39,7 +39,8 @@
 	usb at c5004000 {
 		statuc = "okay";
 		/* VBUS_LAN */
-		nvidia,phy-reset-gpio = <&gpio TEGRA_GPIO(V, 1) GPIO_ACTIVE_HIGH>;
+		nvidia,phy-reset-gpio = <&gpio TEGRA_GPIO(V, 1)
+			GPIO_ACTIVE_LOW>;
 		nvidia,vbus-gpio = <&gpio TEGRA_GPIO(BB, 1) GPIO_ACTIVE_HIGH>;
 	};
 
diff --git a/arch/arm/dts/tegra20-harmony.dts b/arch/arm/dts/tegra20-harmony.dts
index cace74339483..5aec150b5e61 100644
--- a/arch/arm/dts/tegra20-harmony.dts
+++ b/arch/arm/dts/tegra20-harmony.dts
@@ -626,7 +626,8 @@
 
 	usb at c5004000 {
 		status = "okay";
-		nvidia,phy-reset-gpio = <&gpio TEGRA_GPIO(V, 1) 0>;
+		nvidia,phy-reset-gpio = <&gpio TEGRA_GPIO(V, 1)
+			GPIO_ACTIVE_LOW>;
 	};
 
 	usb-phy at c5004000 {
diff --git a/drivers/usb/host/ehci-tegra.c b/drivers/usb/host/ehci-tegra.c
index 31d54ab285bf..c10597861873 100644
--- a/drivers/usb/host/ehci-tegra.c
+++ b/drivers/usb/host/ehci-tegra.c
@@ -600,9 +600,18 @@ static int init_ulpi_usb_controller(struct fdt_usb *config,
 
 	/* reset ULPI phy */
 	if (dm_gpio_is_valid(&config->phy_reset_gpio)) {
-		dm_gpio_set_value(&config->phy_reset_gpio, 0);
-		mdelay(5);
+		/*
+		 * This GPIO is typically active-low, and marked as such in
+		 * device tree. dm_gpio_set_value() takes this into account
+		 * and inverts the value we pass here if required. In other
+		 * words, this first call logically asserts the reset signal,
+		 * which typically results in driving the physical GPIO low,
+		 * and the second call logically de-asserts the reset signal,
+		 * which typically results in driver the GPIO high.
+		 */
 		dm_gpio_set_value(&config->phy_reset_gpio, 1);
+		mdelay(5);
+		dm_gpio_set_value(&config->phy_reset_gpio, 0);
 	}
 
 	/* Reset the usb controller */
-- 
2.9.3