usb: xhci: allow imod-interval to be configurable

The xHCI driver currently has the IMOD set to 160, which
translates to an IMOD interval of 40,000ns (160 * 250)ns

Commit 0cbd4b34cd ("xhci: mediatek: support MTK xHCI host controller")
introduced a QUIRK for the MTK platform to adjust this interval to 20,
which translates to an IMOD interval of 5,000ns (20 * 250)ns. This is
due to the fact that the MTK controller IMOD interval is 8 times
as much as defined in xHCI spec.

Instead of adding more quirk bits for additional platforms, this patch
introduces the ability for vendors to set the IMOD_INTERVAL as is
optimal for their platform. By using device_property_read_u32() on
"imod-interval-ns", the IMOD INTERVAL can be specified in nano seconds.
If no interval is specified, the default of 40,000ns (IMOD=160) will be
used.

No bounds checking has been implemented due to the fact that a vendor
may have violated the spec and would need to specify a value outside of
the max 8,000 IRQs/second limit specified in the xHCI spec.

Tested-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Adam Wallis <awallis@codeaurora.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/mediatek,mtk-xhci.txt

@@ -46,6 +46,7 @@ Optional properties:
  - pinctrl-names : a pinctrl state named "default" must be defined
  - pinctrl-0 : pin control group
 	See: Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
+ - imod-interval-ns: default interrupt moderation interval is 5000ns
 
 Example:
 usb30: usb@11270000 {
@@ -66,6 +67,7 @@ usb30: usb@11270000 {
 	usb3-lpm-capable;
 	mediatek,syscon-wakeup = <&pericfg>;
 	mediatek,wakeup-src = <1>;
+	imod-interval-ns = <10000>;
 };
 
 2nd: dual-role mode with xHCI driver

Documentation/devicetree/bindings/usb/usb-xhci.txt

@@ -31,6 +31,7 @@ Optional properties:
   - usb2-lpm-disable: indicate if we don't want to enable USB2 HW LPM
   - usb3-lpm-capable: determines if platform is USB3 LPM capable
   - quirk-broken-port-ped: set if the controller has broken port disable mechanism
+  - imod-interval-ns: default interrupt moderation interval is 5000ns
 
 Example:
 	usb@f0931000 {

drivers/usb/host/xhci-mtk.c

@@ -674,6 +674,15 @@ static int xhci_mtk_probe(struct platform_device *pdev)
 
 	xhci = hcd_to_xhci(hcd);
 	xhci->main_hcd = hcd;
+
+	/*
+	 * imod_interval is the interrupt moderation value in nanoseconds.
+	 * The increment interval is 8 times as much as that defined in
+	 * the xHCI spec on MTK's controller.
+	 */
+	xhci->imod_interval = 5000;
+	device_property_read_u32(dev, "imod-interval-ns", &xhci->imod_interval);
+
 	xhci->shared_hcd = usb_create_shared_hcd(driver, dev,
 			dev_name(dev), hcd);
 	if (!xhci->shared_hcd) {

drivers/usb/host/xhci-pci.c

@@ -234,6 +234,9 @@ static int xhci_pci_setup(struct usb_hcd *hcd)
 	if (!xhci->sbrn)
 		pci_read_config_byte(pdev, XHCI_SBRN_OFFSET, &xhci->sbrn);
 
+	/* imod_interval is the interrupt moderation value in nanoseconds. */
+	xhci->imod_interval = 40000;
+
 	retval = xhci_gen_setup(hcd, xhci_pci_quirks);
 	if (retval)
 		return retval;

drivers/usb/host/xhci-plat.c

@@ -269,6 +269,11 @@ static int xhci_plat_probe(struct platform_device *pdev)
 	if (device_property_read_bool(&pdev->dev, "quirk-broken-port-ped"))
 		xhci->quirks |= XHCI_BROKEN_PORT_PED;
 
+	/* imod_interval is the interrupt moderation value in nanoseconds. */
+	xhci->imod_interval = 40000;
+	device_property_read_u32(sysdev, "imod-interval-ns",
+				 &xhci->imod_interval);
+
 	hcd->usb_phy = devm_usb_get_phy_by_phandle(sysdev, "usb-phy", 0);
 	if (IS_ERR(hcd->usb_phy)) {
 		ret = PTR_ERR(hcd->usb_phy);

drivers/usb/host/xhci.c

@@ -583,11 +583,7 @@ int xhci_run(struct usb_hcd *hcd)
 			"// Set the interrupt modulation register");
 	temp = readl(&xhci->ir_set->irq_control);
 	temp &= ~ER_IRQ_INTERVAL_MASK;
-	/*
-	 * the increment interval is 8 times as much as that defined
-	 * in xHCI spec on MTK's controller
-	 */
-	temp |= (u32) ((xhci->quirks & XHCI_MTK_HOST) ? 20 : 160);
+	temp |= (xhci->imod_interval / 250) & ER_IRQ_INTERVAL_MASK;
 	writel(temp, &xhci->ir_set->irq_control);
 
 	/* Set the HCD state before we enable the irqs */

drivers/usb/host/xhci.h

@@ -1717,6 +1717,8 @@ struct xhci_hcd {
 	u8		max_interrupters;
 	u8		max_ports;
 	u8		isoc_threshold;
+	/* imod_interval in ns (I * 250ns) */
+	u32		imod_interval;
 	int		event_ring_max;
 	/* 4KB min, 128MB max */
 	int		page_size;