[PATCH 2/2] usb: dwc3: core: improve reset sequence

[Chris Morgan <macroalpha82@gmail.com>]

From: Chris Morgan <macromorgan@hotmail.com>

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).

Note that this patch was submitted to Linux in 2016 [1], however I can
confirm it is needed to support gadget mode in U-Boot on my device.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/patch/drivers/usb/dwc3?id=f59dcab176293b646e1358144c93c58c3cda2813

Suggested-by: Mian Yousaf Kaukab <yousaf.kaukab@intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
---
 drivers/usb/dwc3/core.c | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 847fa1f82c3..b4de2e95a0d 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -59,11 +59,20 @@ 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);
+	/*
+	 * 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;
+
+	reg = dwc3_readl(dwc->regs, DWC3_DCTL);
+	reg |= DWC3_DCTL_CSFTRST;
+	reg &= ~DWC3_DCTL_RUN_STOP;
+	dwc3_gadget_dctl_write_safe(dwc, reg);
 
 	/* Assert USB3 PHY reset */
 	reg = dwc3_readl(dwc->regs, DWC3_GUSB3PIPECTL(0));
@@ -87,12 +96,14 @@ static int dwc3_core_soft_reset(struct dwc3 *dwc)
 	reg &= ~DWC3_GUSB2PHYCFG_PHYSOFTRST;
 	dwc3_writel(dwc->regs, DWC3_GUSB2PHYCFG(0), reg);
 
-	mdelay(100);
+	do {
+		reg = dwc3_readl(dwc->regs, DWC3_DCTL);
+		if (!(reg & DWC3_DCTL_CSFTRST))
+			return 0;
+		udelay(1);
+	} while (--retries);
 
-	/* 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);
+	return -ETIMEDOUT;
 
 	return 0;
 }
@@ -137,7 +148,7 @@ static void dwc3_ref_clk_period(struct dwc3 *dwc)
 
 	if (dwc->ref_clk) {
 		rate = clk_get_rate(dwc->ref_clk);
-		if (!rate)
+		if (!rate || (long)rate < 0)
 			return;
 		period = NSEC_PER_SEC / rate;
 	} else {
-- 
2.43.0