linux-kernel - Re: [PATCH] usbfs: Increase arbitrary limit for USB 3 isopkt length

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Date:	Fri, 24 May 2013 09:51:19 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Federico Manzan <f.manzan@...il.com>
cc:	gregkh@...uxfoundation.org, <sarah.a.sharp@...ux.intel.com>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usbfs: Increase arbitrary limit for USB 3 isopkt length

On Fri, 24 May 2013, Federico Manzan wrote:

> Increase the current arbitrary limit for isocronous packet size to a
> value large enough to account for USB 3.0 super bandwidth streams,
> bMaxBurst (0~15 allowed, 1~16 packets)
> bmAttributes (bit 1:0, mult 0~2, 1~3 packets)
> so the size max for one USB 3 isocronous transfer is
> 1024 byte * 16 * 3 = 49152 byte
> 
> Signed-off-by: Federico Manzan <f.manzan@...il.com>

So you decided to take matters into your own hands.  Good for you!

> diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
> index caefc80..7ac137e 100644
> --- a/drivers/usb/core/devio.c
> +++ b/drivers/usb/core/devio.c
> @@ -1287,9 +1287,11 @@ static int proc_do_submiturb(struct dev_state *ps, struct usbdevfs_urb *uurb,
>  			goto error;
>  		}
>  		for (totlen = u = 0; u < uurb->number_of_packets; u++) {
> -			/* arbitrary limit,
> -			 * sufficient for USB 2.0 high-bandwidth iso */
> -			if (isopkt[u].length > 8192) {
> +			/* arbitrary limit need for USB 3.0
> +			 * bMaxBurst (0~15 allowed, 1~16 packets)
> +			 * bmAttributes (bit 1:0, mult 0~2, 1~3 packets)
> +			 * sizemax: 1024 * 16 * 3 = 49152*/
> +			if (isopkt[u].length > 65536) {
>  				ret = -EINVAL;
>  				goto error;
>  			}

A couple of suggestions for improvements:

First, new or updated multi-line comments should follow the accepted
formatting standard:

	/*
	 * Start comment here...
	 * and end here.
	 */

Second, it's confusing for the comment to mention that the limit is
49152 and the code to set the limit to 65536.  They should agree on a
single value (probably 49152).

If you make those two changes, you can add

Acked-by: Alan Stern <stern@...land.harvard.edu>

Alan Stern

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