[PATCH] usb: dwc3: core: improve reset sequence

[Venkatesh Yadav Abbarapu]

[ Felipe: Ported from Linux kernel commit
	  f59dcab17629 ("usb: dwc3: core: improve reset sequence") ]

According to Synopsys Databook, we shouldn't be
relying on GCTL.CORESOFTRESET bit as that's only for
debugging purposes. Instead, let's use DCTL.CSFTRST
if we're OTG or PERIPHERAL mode.

Host side block will be reset by XHCI driver if
necessary. Note that this reduces amount of time
spent on dwc3_probe() by a long margin.

We're still gonna wait for reset to finish for a
long time (default to 1ms max), but tests show that
the reset polling loop executed at most 19 times
(modprobe dwc3 && modprobe -r dwc3 executed 1000
times in a row).

Without proper core reset, observing random issues like when the USB(DWC3)
is in device mode, the host device is not able to detect the USB device.

Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu at amd.com>
---
 drivers/usb/dwc3/core.c | 49 +++++++++++++++--------------------------
 1 file changed, 18 insertions(+), 31 deletions(-)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 49f6a1900b..6cd0ad4746 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -60,42 +60,29 @@ static void dwc3_set_mode(struct dwc3 *dwc, u32 mode)
 static int dwc3_core_soft_reset(struct dwc3 *dwc)
 {
 	u32		reg;
+	int		retries = 1000;
 
-	/* Before Resetting PHY, put Core in Reset */
-	reg = dwc3_readl(dwc->regs, DWC3_GCTL);
-	reg |= DWC3_GCTL_CORESOFTRESET;
-	dwc3_writel(dwc->regs, DWC3_GCTL, reg);
-
-	/* Assert USB3 PHY reset */
-	reg = dwc3_readl(dwc->regs, DWC3_GUSB3PIPECTL(0));
-	reg |= DWC3_GUSB3PIPECTL_PHYSOFTRST;
-	dwc3_writel(dwc->regs, DWC3_GUSB3PIPECTL(0), reg);
-
-	/* Assert USB2 PHY reset */
-	reg = dwc3_readl(dwc->regs, DWC3_GUSB2PHYCFG(0));
-	reg |= DWC3_GUSB2PHYCFG_PHYSOFTRST;
-	dwc3_writel(dwc->regs, DWC3_GUSB2PHYCFG(0), reg);
-
-	mdelay(100);
-
-	/* Clear USB3 PHY reset */
-	reg = dwc3_readl(dwc->regs, DWC3_GUSB3PIPECTL(0));
-	reg &= ~DWC3_GUSB3PIPECTL_PHYSOFTRST;
-	dwc3_writel(dwc->regs, DWC3_GUSB3PIPECTL(0), reg);
+	/*
+	 * We're resetting only the device side because, if we're in host mode,
+	 * XHCI driver will reset the host block. If dwc3 was configured for
+	 * host-only mode, then we can return early.
+	 */
+	if (dwc->dr_mode == USB_DR_MODE_HOST)
+		return 0;
 
-	/* Clear USB2 PHY reset */
-	reg = dwc3_readl(dwc->regs, DWC3_GUSB2PHYCFG(0));
-	reg &= ~DWC3_GUSB2PHYCFG_PHYSOFTRST;
-	dwc3_writel(dwc->regs, DWC3_GUSB2PHYCFG(0), reg);
+	reg = dwc3_readl(dwc->regs, DWC3_DCTL);
+	reg |= DWC3_DCTL_CSFTRST;
+	dwc3_writel(dwc->regs, DWC3_DCTL, reg);
 
-	mdelay(100);
+	do {
+		reg = dwc3_readl(dwc->regs, DWC3_DCTL);
+		if (!(reg & DWC3_DCTL_CSFTRST))
+			return 0;
 
-	/* After PHYs are stable we can take Core out of reset state */
-	reg = dwc3_readl(dwc->regs, DWC3_GCTL);
-	reg &= ~DWC3_GCTL_CORESOFTRESET;
-	dwc3_writel(dwc->regs, DWC3_GCTL, reg);
+		udelay(1);
+	} while (--retries);
 
-	return 0;
+	return -ETIMEDOUT;
 }
 
 /*
-- 
2.17.1