Re: [PATCH v2 1/5] USB: gadget: f_rndis: fix bitrate for SuperSpeed and above

[William Mcvicker <willmcvicker@google.com>]

On Mon, Nov 30, 2020 at 06:24:40AM +0000, Peter Chen wrote:
> On 20-11-27 15:05:55, Greg Kroah-Hartman wrote:
> > From: Will McVicker <willmcvicker@google.com>
> > 
> > Align the SuperSpeed Plus bitrate for f_rndis to match f_ncm's ncm_bitrate
> > defined by commit 1650113888fe ("usb: gadget: f_ncm: add SuperSpeed descriptors
> > for CDC NCM").
> > 
> > Cc: Felipe Balbi <balbi@kernel.org>
> > Cc: EJ Hsu <ejh@nvidia.com>
> > Cc: Peter Chen <peter.chen@nxp.com>
> > Cc: stable <stable@vger.kernel.org>
> > Signed-off-by: Will McVicker <willmcvicker@google.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > ---
> >  drivers/usb/gadget/function/f_rndis.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/usb/gadget/function/f_rndis.c b/drivers/usb/gadget/function/f_rndis.c
> > index 9534c8ab62a8..0739b05a0ef7 100644
> > --- a/drivers/usb/gadget/function/f_rndis.c
> > +++ b/drivers/usb/gadget/function/f_rndis.c
> > @@ -87,8 +87,10 @@ static inline struct f_rndis *func_to_rndis(struct usb_function *f)
> >  /* peak (theoretical) bulk transfer rate in bits-per-second */
> >  static unsigned int bitrate(struct usb_gadget *g)
> >  {
> > +	if (gadget_is_superspeed(g) && g->speed >= USB_SPEED_SUPER_PLUS)
> > +		return 4250000000U;
> 
> Is tested value or spec defined value?
> 
> >  	if (gadget_is_superspeed(g) && g->speed == USB_SPEED_SUPER)
> > -		return 13 * 1024 * 8 * 1000 * 8;
> > +		return 3750000000U;
> 
> 13 * 1024 * 8 * 1000 * 8 = 851,968,000, how 3750000000U is calculated?
> 
> >  	else if (gadget_is_dualspeed(g) && g->speed == USB_SPEED_HIGH)
> >  		return 13 * 512 * 8 * 1000 * 8;
> >  	else
> > -- 
> > 2.29.2
> > 
> 
> -- 
> 
> Thanks,
> Peter Chen

Hi Peter,

Thanks for the reviews! Regarding the updated transfer rates, please refer to
the f_ncm commit email thread by Lorenzo that explains the reasoning behind
these speeds:

https://patchwork.kernel.org/project/linux-usb/patch/20200818165848.4117493-1-lorenzo@google.com/

Thanks,
Will