Re: [PATCH 16/17] usb: common: add function to get interval expressed in us unit

On Fri, 2021-03-05 at 10:33 -0500, Alan Stern wrote:

On Fri, Mar 05, 2021 at 05:02:54PM +0800, Chunfeng Yun wrote:

quoted

Add a new function to convert bInterval into the time expressed
in 1us unit.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
---

quoted

--- a/drivers/usb/common/common.c
+++ b/drivers/usb/common/common.c

@@ -165,6 +165,39 @@ enum usb_dr_mode usb_get_dr_mode(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(usb_get_dr_mode);
 
+unsigned int usb_decode_interval(const struct usb_endpoint_descriptor *epd,
+				 enum usb_device_speed speed)
+{
+	unsigned int interval = 0;
+
+	switch (usb_endpoint_type(epd)) {
+	case USB_ENDPOINT_XFER_CONTROL:
+		/* uframes per NAK */
+		if (speed == USB_SPEED_HIGH)
+			interval = epd->bInterval;
+		break;
+	case USB_ENDPOINT_XFER_ISOC:
+		interval = 1 << (epd->bInterval - 1);
+		break;
+	case USB_ENDPOINT_XFER_BULK:
+		/* uframes per NAK */
+		if (speed == USB_SPEED_HIGH && usb_endpoint_dir_out(epd))
+			interval = epd->bInterval;
+		break;
+	case USB_ENDPOINT_XFER_INT:
+		if (speed >= USB_SPEED_HIGH)
+			interval = 1 << (epd->bInterval - 1);
+		else
+			interval = epd->bInterval;
+		break;
+	}
+
+	interval *= (speed >= USB_SPEED_HIGH) ? 125 : 1000;
+
+	return interval;
+}
+EXPORT_SYMBOL_GPL(usb_decode_interval);

quoted

--- a/include/linux/usb/ch9.h
+++ b/include/linux/usb/ch9.h

@@ -90,6 +90,17 @@ extern enum usb_ssp_rate usb_get_maximum_ssp_rate(struct device *dev);
  */
 extern const char *usb_state_string(enum usb_device_state state);
 
+/**
+ * usb_decode_interval - Decode bInterval into the time expressed in 1us unit
+ * @epd: The descriptor of the endpoint
+ * @speed: The speed that the endpoint works as
+ *
+ * Function returns the interval expressed in 1us unit for servicing
+ * endpoint for data transfers.
+ */
+unsigned int usb_decode_interval(const struct usb_endpoint_descriptor *epd,
+				 enum usb_device_speed speed);

As a general rule, I believe people expect to find the kerneldoc for a 
function next to the function's definition, not next to the declaration 
in a header file.

Got it, thanks

Alan Stern