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

Alan Stern
2021-03-05T15:34:05Z

On Fri, Mar 05, 2021 at 05:02:54PM +0800, Chunfeng Yun wrote:
> Add a new function to convert bInterval into the time expressed
> in 1us unit.
>
> Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
> ---

> --- 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);

> --- 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.

Alan Stern