linux-kernel - Re: [PATCH 2/3] usb: gadget: f_sourcesink support for maxburst for bulk transfers

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Message-ID: <cf2940e3-5430-4e84-916b-608c33028a7c@rowland.harvard.edu>
Date: Fri, 4 Jul 2025 09:47:30 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Srikanth Chary Chennoju <srikanth.chary-chennoju@....com>
Cc: gregkh@...uxfoundation.org, Thinh.Nguyen@...opsys.com,
	m.grzeschik@...gutronix.de, Chris.Wulff@...mp.com, tiwai@...e.de,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	punnaiah.choudary.kalluri@....com
Subject: Re: [PATCH 2/3] usb: gadget: f_sourcesink support for maxburst for
 bulk transfers

On Fri, Jul 04, 2025 at 05:10:12PM +0530, Srikanth Chary Chennoju wrote:
> This patch supports bulk_maxburst. Without this change
> we are not able to achieve performance for super speed plus device.
> Without this fix, we confirmed through lecroy that it is sending
> packets with NumP always equal to 1.
> 
> Signed-off-by: Srikanth Chary Chennoju <srikanth.chary-chennoju@....com>
> ---
>  drivers/usb/gadget/function/f_sourcesink.c | 14 ++++++++++++++
>  drivers/usb/gadget/function/g_zero.h       |  2 ++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/drivers/usb/gadget/function/f_sourcesink.c b/drivers/usb/gadget/function/f_sourcesink.c
> index ec5fd25020fd..84f3b3bc7669 100644
> --- a/drivers/usb/gadget/function/f_sourcesink.c
> +++ b/drivers/usb/gadget/function/f_sourcesink.c

> @@ -341,6 +346,14 @@ sourcesink_bind(struct usb_configuration *c, struct usb_function *f)
>  	if (!ss->out_ep)
>  		goto autoconf_fail;
>  
> +	/*
> +	 * Fill in the SS bulk descriptors from the module parameters.
> +	 * We assume that the user knows what they are doing and won't
> +	 * give parameters that their UDC doesn't support.
> +	 */

That's not such a great assumption; people make mistakes like this quite 
a lot.  If checking and adjusting the parameters isn't terribly 
difficult, you should do it.

Alan Stern