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

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.
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Link: https://lore.kernel.org/r/20200913215926.29880-1-chris.packham@alliedtelesis.co.nzSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ehci-platform.c

@@ -42,6 +42,9 @@
 #define EHCI_MAX_CLKS 4
 #define hcd_to_ehci_priv(h) ((struct ehci_platform_priv *)hcd_to_ehci(h)->priv)
 
+#define BCM_USB_FIFO_THRESHOLD	0x00800040
+#define bcm_iproc_insnreg01	hostpc[0]
+
 struct ehci_platform_priv {
 	struct clk *clks[EHCI_MAX_CLKS];
 	struct reset_control *rsts;
@@ -75,6 +78,11 @@ static int ehci_platform_reset(struct usb_hcd *hcd)
 
 	if (pdata->no_io_watchdog)
 		ehci->need_io_watchdog = 0;
+
+	if (of_device_is_compatible(pdev->dev.of_node, "brcm,xgs-iproc-ehci"))
+		ehci_writel(ehci, BCM_USB_FIFO_THRESHOLD,
+			    &ehci->regs->bcm_iproc_insnreg01);
+
 	return 0;
 }