[PATCH v2] usb: dwc3: Toggle GCTL.CORESOFTRESET as a first step

[Andrey Smirnov <andrew.smirnov@gmail.com>]

Toggle GCTL.CORESOFTRESET before trying to access any of the block's
registers. Without this additional step, first read of DWC3_GHWPARAMS*
that follows results in assertion of GSTS.CSRTIMEOUT and IP block
stuck in a non-functional state.

Note that all above has only been observerd on i.MX8MQ (ZII Zest
board) for USB1 controller. USB2 doesn't seem to be affected by this.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
---

Changes since [v1]:

    - Dropped 100 ms delay
    
[v1] http://lists.infradead.org/pipermail/barebox/2019-March/037501.html

 drivers/usb/dwc3/core.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 2e7031a34..60fd6318d 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -663,6 +663,25 @@ static void dwc3_check_params(struct dwc3 *dwc)
 	}
 }
 
+static void dwc3_coresoft_reset(struct dwc3 *dwc)
+{
+	u32 reg;
+
+	reg = dwc3_readl(dwc->regs, DWC3_GCTL);
+	reg |= DWC3_GCTL_CORESOFTRESET;
+	dwc3_writel(dwc->regs, DWC3_GCTL, reg);
+
+	/*
+	 * Similar reset sequence in U-Boot has a 100ms delay here. In
+	 * practice reset sequence seem to work as expected even
+	 * without a delay.
+	 */
+
+	reg = dwc3_readl(dwc->regs, DWC3_GCTL);
+	reg &= ~DWC3_GCTL_CORESOFTRESET;
+	dwc3_writel(dwc->regs, DWC3_GCTL, reg);
+}
+
 static int dwc3_probe(struct device_d *dev)
 {
 	struct dwc3		*dwc;
@@ -695,6 +714,8 @@ static int dwc3_probe(struct device_d *dev)
 	if (ret)
 		return ret;
 
+	dwc3_coresoft_reset(dwc);
+
 	dwc3_cache_hwparams(dwc);
 
 	ret = dwc3_core_init(dwc);
-- 
2.20.1


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