On Mon, Oct 09, 2023 at 07:50:05PM +0530, Krishna Kurapati wrote:
> Currently the NCM driver restricts wMaxSegmentSize that indicates
> the datagram size coming from network layer to 1514.
I don't see that restriction in the existing driver, where does that
happen?
> However the spec doesn't have any limitation.
What spec?
> For P2P connections over NCM, increasing MTU helps increasing
> throughput.
While increasing latency, right?
> Add support to configure this value before configfs symlink is
> created. Also since the NTB Out/In buffer sizes are fixed at 16384
> bytes, limit the segment size to an upper cap of 15014. Set the
> default MTU size for the ncm interface during function bind before
> network interface is registered allowing MTU to be set in parity
> with wMaxSegmentSize.
Where does 15014 come from?
>
> Signed-off-by: Krishna Kurapati <quic_kriskura@xxxxxxxxxxx>
> ---
> drivers/usb/gadget/function/f_ncm.c | 51 +++++++++++++++++++++++++++++
> drivers/usb/gadget/function/u_ncm.h | 2 ++
> 2 files changed, 53 insertions(+)
>
> diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c
> index feccf4c8cc4f..eab297b22200 100644
> --- a/drivers/usb/gadget/function/f_ncm.c
> +++ b/drivers/usb/gadget/function/f_ncm.c
> @@ -103,6 +103,8 @@ static inline struct f_ncm *func_to_ncm(struct usb_function *f)
> /* Delay for the transmit to wait before sending an unfilled NTB frame. */
> #define TX_TIMEOUT_NSECS 300000
>
> +#define MAX_DATAGRAM_SIZE 15014
Where does this magic value come from? Please document it really really
well.
> +
> #define FORMATS_SUPPORTED (USB_CDC_NCM_NTB16_SUPPORTED | \
> USB_CDC_NCM_NTB32_SUPPORTED)
>
> @@ -1408,6 +1410,7 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
> ncm_opts = container_of(f->fi, struct f_ncm_opts, func_inst);
>
> if (cdev->use_os_string) {
> + ncm_opts->net->mtu = (ncm_opts->max_segment_size - ETH_HLEN);
> f->os_desc_table = kzalloc(sizeof(*f->os_desc_table),
> GFP_KERNEL);
> if (!f->os_desc_table)
> @@ -1469,6 +1472,8 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
>
> status = -ENODEV;
>
> + ecm_desc.wMaxSegmentSize = ncm_opts->max_segment_size;
> +
> /* allocate instance-specific endpoints */
> ep = usb_ep_autoconfig(cdev->gadget, &fs_ncm_in_desc);
> if (!ep)
> @@ -1569,11 +1574,56 @@ USB_ETHERNET_CONFIGFS_ITEM_ATTR_QMULT(ncm);
> /* f_ncm_opts_ifname */
> USB_ETHERNET_CONFIGFS_ITEM_ATTR_IFNAME(ncm);
>
> +static ssize_t ncm_opts_max_segment_size_show(struct config_item *item,
> + char *page)
> +{
> + struct f_ncm_opts *opts = to_f_ncm_opts(item);
> + u32 segment_size;
> +
> + mutex_lock(&opts->lock);
> + segment_size = opts->max_segment_size;
> + mutex_unlock(&opts->lock);
> +
> + return sprintf(page, "%u\n", segment_size);
sysfs_emit()?
thanks,
greg k-h
