On Mon, Aug 24, 2020 at 10:55 PM Lorenzo Colitti <lorenzo@xxxxxxxxxx> wrote:
>
> Currently, SuperSpeed NCM gadgets report a speed of 851 Mbps
> in USB_CDC_NOTIFY_SPEED_CHANGE. But the calculation appears to
> assume 16 packets per microframe, and USB 3 and above no longer
> use microframes.
>
> Maximum speed is actually much higher. On a direct connection,
> theoretical throughput is at most 3.86 Gbps for gen1x1 and
> 9.36 Gbps for gen2x1, and I have seen gadget->host iperf
> throughput of >2 Gbps for gen1x1 and >4 Gbps for gen2x1.
>
> Unfortunately the ConnectionSpeedChange defined in the CDC spec
> only uses 32-bit values, so we can't report accurate numbers for
> 10Gbps and above. So, report 3.75Gbps for SuperSpeed (which is
> roughly maximum theoretical performance) and 4.25Gbps for
> SuperSpeed Plus (which is close to the maximum that we can report
> in a 32-bit unsigned integer).
>
> This results in:
>
> [50879.191272] cdc_ncm 2-2:1.0 enx228b127e050c: renamed from usb0
> [50879.234778] cdc_ncm 2-2:1.0 enx228b127e050c: 3750 mbit/s downlink 3750 mbit/s uplink
>
> on SuperSpeed and:
>
> [50798.434527] cdc_ncm 8-2:1.0 enx228b127e050c: renamed from usb0
> [50798.524278] cdc_ncm 8-2:1.0 enx228b127e050c: 4250 mbit/s downlink 4250 mbit/s uplink
>
> on SuperSpeed Plus.
>
> Fixes: 1650113888fe ("usb: gadget: f_ncm: add SuperSpeed descriptors for CDC NCM")
> Signed-off-by: Lorenzo Colitti <lorenzo@xxxxxxxxxx>
> ---
> drivers/usb/gadget/function/f_ncm.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c
> index 1d900081b1..5b9266a87f 100644
> --- a/drivers/usb/gadget/function/f_ncm.c
> +++ b/drivers/usb/gadget/function/f_ncm.c
> @@ -85,8 +85,10 @@ static inline struct f_ncm *func_to_ncm(struct usb_function *f)
> /* peak (theoretical) bulk transfer rate in bits-per-second */
> static inline unsigned ncm_bitrate(struct usb_gadget *g)
> {
> - if (gadget_is_superspeed(g) && g->speed == USB_SPEED_SUPER)
> - return 13 * 1024 * 8 * 1000 * 8;
> + if (gadget_is_superspeed(g) && g->speed >= USB_SPEED_SUPER_PLUS)
> + return 4250000000U;
> + else if (gadget_is_superspeed(g) && g->speed == USB_SPEED_SUPER)
> + return 3750000000U;
> else if (gadget_is_dualspeed(g) && g->speed == USB_SPEED_HIGH)
> return 13 * 512 * 8 * 1000 * 8;
> else
> --
> 2.28.0.297.g1956fa8f8d-goog
>
Reviewed-by: Maciej Żenczykowski <maze@xxxxxxxxxx>
