usb: dwc3: add power down scale setting

Some SoC(e.g NXP imx8MQ) may have a wrong default power down scale
setting so need init it to be the correct value, the power down
scale setting description in DWC3 databook:

Power Down Scale (PwrDnScale)
The USB3 suspend_clk input replaces pipe3_rx_pclk as a clock source to
a small part of the USB3 core that operates when the SS PHY is in its
lowest power (P3) state, and therefore does not provide a clock.
The Power Down Scale field specifies how many suspend_clk periods fit
into a 16 kHz clock period. When performing the division, round up the
remainder.
For example, when using an 8-bit/16-bit/32-bit PHY and 25-MHz Suspend
clock,
Power Down Scale = 25000 kHz/16 kHz = 13'd1563 (rounder up)

So use the suspend clock rate to calculate it.
Reviewed-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Signed-off-by: Li Jun <jun.li@nxp.com>
Link: https://lore.kernel.org/r/1654568404-3461-1-git-send-email-jun.li@nxp.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc3/core.c

@@ -1029,6 +1029,37 @@ static void dwc3_set_incr_burst_type(struct dwc3 *dwc)
 	dwc3_writel(dwc->regs, DWC3_GSBUSCFG0, cfg);
 }
 
+static void dwc3_set_power_down_clk_scale(struct dwc3 *dwc)
+{
+	u32 scale;
+	u32 reg;
+
+	if (!dwc->susp_clk)
+		return;
+
+	/*
+	 * The power down scale field specifies how many suspend_clk
+	 * periods fit into a 16KHz clock period. When performing
+	 * the division, round up the remainder.
+	 *
+	 * The power down scale value is calculated using the fastest
+	 * frequency of the suspend_clk. If it isn't fixed (but within
+	 * the accuracy requirement), the driver may not know the max
+	 * rate of the suspend_clk, so only update the power down scale
+	 * if the default is less than the calculated value from
+	 * clk_get_rate() or if the default is questionably high
+	 * (3x or more) to be within the requirement.
+	 */
+	scale = DIV_ROUND_UP(clk_get_rate(dwc->susp_clk), 16000);
+	reg = dwc3_readl(dwc->regs, DWC3_GCTL);
+	if ((reg & DWC3_GCTL_PWRDNSCALE_MASK) < DWC3_GCTL_PWRDNSCALE(scale) ||
+	    (reg & DWC3_GCTL_PWRDNSCALE_MASK) > DWC3_GCTL_PWRDNSCALE(scale*3)) {
+		reg &= ~(DWC3_GCTL_PWRDNSCALE_MASK);
+		reg |= DWC3_GCTL_PWRDNSCALE(scale);
+		dwc3_writel(dwc->regs, DWC3_GCTL, reg);
+	}
+}
+
 /**
  * dwc3_core_init - Low-level initialization of DWC3 Core
  * @dwc: Pointer to our controller context structure
@@ -1105,6 +1136,9 @@ static int dwc3_core_init(struct dwc3 *dwc)
 	if (ret)
 		goto err1;
 
+	/* Set power down scale of suspend_clk */
+	dwc3_set_power_down_clk_scale(dwc);
+
 	/* Adjust Frame Length */
 	dwc3_frame_length_adjustment(dwc);
 

drivers/usb/dwc3/core.h

@@ -231,6 +231,7 @@
 
 /* Global Configuration Register */
 #define DWC3_GCTL_PWRDNSCALE(n)	((n) << 19)
+#define DWC3_GCTL_PWRDNSCALE_MASK	GENMASK(31, 19)
 #define DWC3_GCTL_U2RSTECN	BIT(16)
 #define DWC3_GCTL_RAMCLKSEL(x)	(((x) & DWC3_GCTL_CLK_MASK) << 6)
 #define DWC3_GCTL_CLK_BUS	(0)