[PATCH] usb: host: ehci-platform: Add workaround for brcm,xgs-iproc-ehci

[Chris Packham <chris.packham@alliedtelesis.co.nz>]

The ehci controller found in some Broadcom switches with integrated SoCs
has an issue which causes a soft lockup with large transfers like you
see when running ext4 on USB3 flash drive.

Port the fix from the Broadcom XLDK to increase the OUT_THRESHOLD to
avoid the problem.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
---

I don't have much data on what this change does. I can say it is needed to
avoid a soft lockup when using a USB3 Flash drive formatted has ext4 (USB2 +
ext4 is OK, USB3 + fat is OK). I presume the affected combination ends up using
larger transfers triggering the problem.

The equivalent change in the Broadcom XLDK is

	if (IS_ENABLED(CONFIG_USB_EHCI_XGS_IPROC))
		ehci_writel(ehci, BCM_USB_FIFO_THRESHOLD,
				&ehci->regs->reserved4[6]);

This is problematic because it would unconditionally apply to all ehci
controllers whenever CONFIG_USB_EHCI_XGS_IPROC is enabled (also reserved4 only
goes to 6 so technically it's indexing off the end of the array).

I wasn't sure if I should add a new property or somehow detect the affected
host controller. I settled on using of_device_is_compatible() as that seemed
the simplest thing to do.

 drivers/usb/host/ehci-platform.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/usb/host/ehci-platform.c b/drivers/usb/host/ehci-platform.c
index 006c4f6188a5..0d2de8faa3c1 100644
--- a/drivers/usb/host/ehci-platform.c
+++ b/drivers/usb/host/ehci-platform.c
@@ -53,6 +53,9 @@ struct ehci_platform_priv {
 
 static const char hcd_name[] = "ehci-platform";
 
+#define bcm_iproc_insnreg01	hostpc
+#define BCM_USB_FIFO_THRESHOLD	0x00800040
+
 static int ehci_platform_reset(struct usb_hcd *hcd)
 {
 	struct platform_device *pdev = to_platform_device(hcd->self.controller);
@@ -358,6 +361,9 @@ static int ehci_platform_probe(struct platform_device *dev)
 
 	device_wakeup_enable(hcd->self.controller);
 	device_enable_async_suspend(hcd->self.controller);
+	if (of_device_is_compatible(dev->dev.of_node, "brcm,xgs-iproc-ehci"))
+		ehci_writel(ehci, BCM_USB_FIFO_THRESHOLD,
+			    ehci->regs->bcm_iproc_insnreg01);
 	platform_set_drvdata(dev, hcd);
 
 	if (priv->quirk_poll)
-- 
2.28.0