[PATCH v2 2/2] usb: host: ehci-tegra: Avoid getting the same reset twice

[Thierry Reding]

From: Thierry Reding <treding@xxxxxxxxxx>

Starting with commit 0b52297f2288 ("reset: Add support for shared reset
controls") there is a reference count for reset control assertions. The
goal is to allow resets to be shared by multiple devices and an assert
will take effect only when all instances have asserted the reset.

In order to preserve backwards-compatibility, all reset controls become
exclusive by default. This is to ensure that reset_control_assert() can
immediately assert in hardware.

However, this new behaviour triggers the following warning in the EHCI
driver for Tegra:

[    3.365019] ------------[ cut here ]------------
[    3.369639] WARNING: CPU: 0 PID: 1 at drivers/reset/core.c:187 __of_reset_control_get+0x16c/0x23c
[    3.382151] Modules linked in:
[    3.385214] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.6.0-rc6-next-20160503 #140
[    3.392769] Hardware name: NVIDIA Tegra SoC (Flattened Device Tree)
[    3.399046] [<c010fa50>] (unwind_backtrace) from [<c010b120>] (show_stack+0x10/0x14)
[    3.406787] [<c010b120>] (show_stack) from [<c0347dcc>] (dump_stack+0x90/0xa4)
[    3.414007] [<c0347dcc>] (dump_stack) from [<c011f4fc>] (__warn+0xe8/0x100)
[    3.420964] [<c011f4fc>] (__warn) from [<c011f5c4>] (warn_slowpath_null+0x20/0x28)
[    3.428525] [<c011f5c4>] (warn_slowpath_null) from [<c03cc8cc>] (__of_reset_control_get+0x16c/0x23c)
[    3.437648] [<c03cc8cc>] (__of_reset_control_get) from [<c0526858>] (tegra_ehci_probe+0x394/0x518)
[    3.446600] [<c0526858>] (tegra_ehci_probe) from [<c04516d8>] (platform_drv_probe+0x4c/0xb0)
[    3.455029] [<c04516d8>] (platform_drv_probe) from [<c044fe78>] (driver_probe_device+0x1ec/0x330)
[    3.463892] [<c044fe78>] (driver_probe_device) from [<c0450074>] (__driver_attach+0xb8/0xbc)
[    3.472320] [<c0450074>] (__driver_attach) from [<c044e1ec>] (bus_for_each_dev+0x68/0x9c)
[    3.480489] [<c044e1ec>] (bus_for_each_dev) from [<c044f338>] (bus_add_driver+0x1a0/0x218)
[    3.488743] [<c044f338>] (bus_add_driver) from [<c0450768>] (driver_register+0x78/0xf8)
[    3.496738] [<c0450768>] (driver_register) from [<c010178c>] (do_one_initcall+0x40/0x170)
[    3.504909] [<c010178c>] (do_one_initcall) from [<c0c00ddc>] (kernel_init_freeable+0x158/0x1f8)
[    3.513600] [<c0c00ddc>] (kernel_init_freeable) from [<c0810784>] (kernel_init+0x8/0x114)
[    3.521770] [<c0810784>] (kernel_init) from [<c0107778>] (ret_from_fork+0x14/0x3c)
[    3.529361] ---[ end trace 4bda87dbe4ecef8a ]---

The reason is that the EHCI implements three ports, each with a separate
reset line. However the first port's reset also serves as a means to
reset the UTMI pad for all ports. There is special code in the driver to
assert and deassert this shared reset at probe time. It needs to do this
regardless of which port is probed first. Unfortunately this means that
if the first port is probed first, it will request its own reset line
and subsequently request the same reset line again (temporarily) to
perform the reset. This used to work fine before the above-mentioned
commit, but now triggers the new WARN.

Work around this by making sure we reuse the port's reset if it happens
to be the same as the UTMI pad reset.

Cc: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>
Cc: Hans de Goede <hdegoede@xxxxxxxxxx>
Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
---
Changes in v2:
- restore has_utmi_pad_registers condition (Alan Stern)

 drivers/usb/host/ehci-tegra.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/host/ehci-tegra.c b/drivers/usb/host/ehci-tegra.c
index c1c1024a054c..8396b622f238 100644
--- a/drivers/usb/host/ehci-tegra.c
+++ b/drivers/usb/host/ehci-tegra.c
@@ -81,15 +81,23 @@ static int tegra_reset_usb_controller(struct platform_device *pdev)
 	struct usb_hcd *hcd = platform_get_drvdata(pdev);
 	struct tegra_ehci_hcd *tegra =
 		(struct tegra_ehci_hcd *)hcd_to_ehci(hcd)->priv;
+	bool has_utmi_pad_registers = false;
 
 	phy_np = of_parse_phandle(pdev->dev.of_node, "nvidia,phy", 0);
 	if (!phy_np)
 		return -ENOENT;
 
+	if (of_property_read_bool(phy_np, "nvidia,has-utmi-pad-registers"))
+		has_utmi_pad_registers = true;
+
 	if (!usb1_reset_attempted) {
 		struct reset_control *usb1_reset;
 
-		usb1_reset = of_reset_control_get(phy_np, "utmi-pads");
+		if (!has_utmi_pad_registers)
+			usb1_reset = of_reset_control_get(phy_np, "utmi-pads");
+		else
+			usb1_reset = tegra->rst;
+
 		if (IS_ERR(usb1_reset)) {
 			dev_warn(&pdev->dev,
 				 "can't get utmi-pads reset from the PHY\n");
@@ -101,11 +109,13 @@ static int tegra_reset_usb_controller(struct platform_device *pdev)
 			reset_control_deassert(usb1_reset);
 		}
 
-		reset_control_put(usb1_reset);
+		if (!has_utmi_pad_registers)
+			reset_control_put(usb1_reset);
+
 		usb1_reset_attempted = true;
 	}
 
-	if (!of_property_read_bool(phy_np, "nvidia,has-utmi-pad-registers")) {
+	if (!has_utmi_pad_registers) {
 		reset_control_assert(tegra->rst);
 		udelay(1);
 		reset_control_deassert(tegra->rst);
-- 
2.8.0