usb: dwc3: ulpi: Use VStsDone to detect PHY regs access completion

In accordance with [1] the DWC_usb3 core sets the GUSB2PHYACCn.VStsDone
bit when the PHY vendor control access is done and clears it when the
application initiates a new transaction. The doc doesn't say anything
about the GUSB2PHYACCn.VStsBsy flag serving for the same purpose. Moreover
we've discovered that the VStsBsy flag can be cleared before the VStsDone
bit. So using the former as a signal of the PHY control registers
completion might be dangerous. Let's have the VStsDone flag utilized
instead then.

[1] Synopsys DesignWare Cores SuperSpeed USB 3.0 xHCI Host Controller
    Databook, 2.70a, December 2013, p.388

Fixes: 88bc9d19 ("usb: dwc3: add ULPI interface support")
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20201210085008.13264-2-Sergey.Semin@baikalelectronics.ru
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc3/core.h

@@ -285,6 +285,7 @@
 
 /* Global USB2 PHY Vendor Control Register */
 #define DWC3_GUSB2PHYACC_NEWREGREQ	BIT(25)
+#define DWC3_GUSB2PHYACC_DONE		BIT(24)
 #define DWC3_GUSB2PHYACC_BUSY		BIT(23)
 #define DWC3_GUSB2PHYACC_WRITE		BIT(22)
 #define DWC3_GUSB2PHYACC_ADDR(n)	(n << 16)

drivers/usb/dwc3/ulpi.c

@@ -24,7 +24,7 @@ static int dwc3_ulpi_busyloop(struct dwc3 *dwc)
 
 	while (count--) {
 		reg = dwc3_readl(dwc->regs, DWC3_GUSB2PHYACC(0));
-		if (!(reg & DWC3_GUSB2PHYACC_BUSY))
+		if (reg & DWC3_GUSB2PHYACC_DONE)
 			return 0;
 		cpu_relax();
 	}