usb: xhci-plat: Add DT parameter to program xhci imod_interval

XHCI allows interrupt moderation using imod_interval at 250ns
increments. Add DT parameter to specify this imod_value for
targets mainly with single CPU to reduce CPU interrupt loads.
This allows better balance between CPU usage and performance.

CRs-fixed: 1019219
Change-Id: Id479c162da6492caff4dd83de4054fee63b6abc5
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>

Documentation/devicetree/bindings/usb/dwc3.txt

@@ -60,6 +60,7 @@ Optional properties:
  - snps,num-normal-evt-buffs: If present, specifies number of normal event buffers. Default is 1.
  - snps,num-gsi-evt-buffs: If present, specifies number of GSI based hardware accelerated event buffers.
 	1 event buffer is needed per h/w accelerated endpoint.
+ - xhci-imod-value: Interrupt moderation interval for host mode (in increments of 250nsec).
 
 This is usually a subnode to DWC3 glue to which it is connected.
 
@@ -74,4 +75,5 @@ dwc3@4a030000 {
 	tx-fifo-resize;
 	snps,usb3-u1u2-disable;
 	snps,num-gsi-evt-buffs = <0x2>;
+	xhci-imod-value = <4000>;
 };

drivers/usb/dwc3/host.c

@@ -25,6 +25,7 @@ int dwc3_host_init(struct dwc3 *dwc)
 	struct platform_device	*xhci;
 	struct usb_xhci_pdata	pdata;
 	int			ret;
+	struct device_node	*node = dwc->dev->of_node;
 
 	xhci = platform_device_alloc("xhci-hcd", PLATFORM_DEVID_AUTO);
 	if (!xhci) {
@@ -52,6 +53,11 @@ int dwc3_host_init(struct dwc3 *dwc)
 
 	pdata.usb3_lpm_capable = dwc->usb3_lpm_capable;
 
+	ret = of_property_read_u32(node, "xhci-imod-value",
+					   &pdata.imod_interval);
+	if (ret)
+		pdata.imod_interval = 0;	/* use default xhci.c value */
+
 	ret = platform_device_add_data(xhci, &pdata, sizeof(pdata));
 	if (ret) {
 		dev_err(dwc->dev, "couldn't add platform data to xHCI device\n");

drivers/usb/host/xhci-plat.c

@@ -138,6 +138,8 @@ static int xhci_plat_probe(struct platform_device *pdev)
 	struct clk              *clk;
 	int			ret;
 	int			irq;
+	u32			temp, imod;
+	unsigned long		flags;
 
 	if (usb_disabled())
 		return -ENODEV;
@@ -256,6 +258,18 @@ static int xhci_plat_probe(struct platform_device *pdev)
 
 	device_wakeup_enable(&xhci->shared_hcd->self.root_hub->dev);
 
+	/* override imod interval if specified */
+	if (pdata && pdata->imod_interval) {
+		imod = pdata->imod_interval & ER_IRQ_INTERVAL_MASK;
+		spin_lock_irqsave(&xhci->lock, flags);
+		temp = readl_relaxed(&xhci->ir_set->irq_control);
+		temp &= ~ER_IRQ_INTERVAL_MASK;
+		temp |= imod;
+		writel_relaxed(temp, &xhci->ir_set->irq_control);
+		spin_unlock_irqrestore(&xhci->lock, flags);
+		dev_dbg(&pdev->dev, "%s: imod set to %u\n", __func__, imod);
+	}
+
 	ret = device_create_file(&pdev->dev, &dev_attr_config_imod);
 	if (ret)
 		dev_err(&pdev->dev, "%s: unable to create imod sysfs entry\n",

include/linux/usb/xhci_pdriver.h

@@ -19,9 +19,13 @@
  * @usb3_lpm_capable:	determines if this xhci platform supports USB3
  *			LPM capability
  *
+ * @imod_interval:	minimum inter-interrupt interval. Specified in
+ *			250nsec increments.
+ *
  */
 struct usb_xhci_pdata {
 	unsigned	usb3_lpm_capable:1;
+	unsigned	imod_interval;
 };
 
 #endif /* __USB_CORE_XHCI_PDRIVER_H */