Re: [PATCH v3 3/4] USB: Add a function to obtain USB version independent maximum bpi value

[Alan Stern <stern@rowland.harvard.edu>]

On Thu, Aug 07, 2025 at 08:53:54AM +0300, Sakari Ailus wrote:
> From: "Rai, Amardeep" <amardeep.rai@intel.com>
> 
> Add usb_endpoint_max_isoc_bpi() to obtain maximum bytes per interval for
> isochronous endpoints in a USB version independent way.

Is "bpi" really a commonly recognized acronym?  Offhand, I wouldn't 
guess that it stands for "bytes per interval".  Can you come up with a 
more explicit name?

> Signed-off-by: Rai, Amardeep <amardeep.rai@intel.com>
> Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
> Co-developed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> Reviewed-by: Hans de Goede <hansg@kernel.org>
> ---
>  include/linux/usb.h | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/include/linux/usb.h b/include/linux/usb.h
> index 535ac37198a1..da0f51dfe15f 100644
> --- a/include/linux/usb.h
> +++ b/include/linux/usb.h
> @@ -2049,6 +2049,37 @@ static inline int usb_translate_errors(int error_code)
>  	}
>  }
>  
> +/**
> + * usb_endpoint_max_isoc_bpi - Get maximum isochronous transfer bytes per interval
> + * @dev: The USB device
> + * @ep: The endpoint
> + *
> + * Returns: the maximum number of bytes isochronous endpoint @endpoint can
> + * transfer in during a service interval, or 0 for non-isochronous endpoints.
> + */
> +static inline u32 usb_endpoint_max_isoc_bpi(struct usb_device *dev,
> +					    const struct usb_host_endpoint *ep)
> +{
> +	if (usb_endpoint_type(&ep->desc) != USB_ENDPOINT_XFER_ISOC)
> +		return 0;
> +
> +	switch (dev->speed) {
> +	case USB_SPEED_SUPER_PLUS:
> +		if (USB_SS_SSP_ISOC_COMP(ep->ss_ep_comp.bmAttributes))
> +			return le32_to_cpu(ep->ssp_isoc_ep_comp.dwBytesPerInterval);
> +		fallthrough;
> +	case USB_SPEED_SUPER:
> +		return le16_to_cpu(ep->ss_ep_comp.wBytesPerInterval);
> +	case USB_SPEED_HIGH:
> +		if (ep->eusb2_isoc_ep_comp.bDescriptorType &&
> +		    !usb_endpoint_maxp(&ep->desc) && usb_endpoint_dir_in(&ep->desc))
> +			return le32_to_cpu(ep->eusb2_isoc_ep_comp.dwBytesPerInterval);
> +		fallthrough;
> +	default:
> +		return usb_endpoint_maxp(&ep->desc) * usb_endpoint_maxp_mult(&ep->desc);
> +	}
> +}

This function is complicated enough that it probably should not be an 
inline routine.  Not unless it's used in only one place (in which case 
why define it in a .h file?).

Alan Stern