xhci: Add helper to set an interrupters interrupt moderation interval

Add a helper to set the interrupt moderation interval for an interrupter.
Each interrupter can have its own moderation value.

Hardware has a 16bit register for the moderation value, each step is 250ns.

Helper function imod_interval argument is in nanoseconds.

Values from 0 to 16383750 (250 x 0xffff) are accepted.
0 means no interrupt throttling.
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
Link: https://lore.kernel.org/r/20240217001017.29969-3-quic_wcheng@quicinc.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci.c

@@ -346,6 +346,23 @@ static int xhci_disable_interrupter(struct xhci_interrupter *ir)
 	return 0;
 }
 
+/* interrupt moderation interval imod_interval in nanoseconds */
+static int xhci_set_interrupter_moderation(struct xhci_interrupter *ir,
+					   u32 imod_interval)
+{
+	u32 imod;
+
+	if (!ir || !ir->ir_set || imod_interval > U16_MAX * 250)
+		return -EINVAL;
+
+	imod = readl(&ir->ir_set->irq_control);
+	imod &= ~ER_IRQ_INTERVAL_MASK;
+	imod |= (imod_interval / 250) & ER_IRQ_INTERVAL_MASK;
+	writel(imod, &ir->ir_set->irq_control);
+
+	return 0;
+}
+
 static void compliance_mode_recovery(struct timer_list *t)
 {
 	struct xhci_hcd *xhci;
@@ -528,7 +545,6 @@ static int xhci_run_finished(struct xhci_hcd *xhci)
  */
 int xhci_run(struct usb_hcd *hcd)
 {
-	u32 temp;
 	u64 temp_64;
 	int ret;
 	struct xhci_hcd *xhci = hcd_to_xhci(hcd);
@@ -551,12 +567,7 @@ int xhci_run(struct usb_hcd *hcd)
 	xhci_dbg_trace(xhci, trace_xhci_dbg_init,
 			"ERST deq = 64'h%0lx", (long unsigned int) temp_64);
 
-	xhci_dbg_trace(xhci, trace_xhci_dbg_init,
-			"// Set the interrupt modulation register");
-	temp = readl(&ir->ir_set->irq_control);
-	temp &= ~ER_IRQ_INTERVAL_MASK;
-	temp |= (xhci->imod_interval / 250) & ER_IRQ_INTERVAL_MASK;
-	writel(temp, &ir->ir_set->irq_control);
+	xhci_set_interrupter_moderation(ir, xhci->imod_interval);
 
 	if (xhci->quirks & XHCI_NEC_HOST) {
 		struct xhci_command *command;