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

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Date:   Mon, 8 Mar 2021 10:02:23 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Alan Stern <stern@...land.harvard.edu>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Ikjoon Jang <ikjn@...omium.org>,
        "Matthias Brugger" <matthias.bgg@...il.com>,
        <linux-usb@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Eddie Hung <eddie.hung@...iatek.com>
Subject: Re: [PATCH 16/17] usb: common: add function to get interval
 expressed in us unit

On Fri, 2021-03-05 at 16:47 +0100, Greg Kroah-Hartman wrote:
> On Fri, Mar 05, 2021 at 10:33:12AM -0500, Alan Stern wrote:
> > 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@...iatek.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.
> 
> I was going to make the same review comment, but if you look above this
> in that file, there's other kernel doc information in the .h file, so
> this does match with the style of the file :(
> 
> We can fix that all up later.
I'll prepare a patch

Thank you
> 
> thanks,
> 
> greg k-h