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

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Date:	Fri, 24 May 2013 17:36:10 +0200
From:	Federico Manzan <f.manzan@...il.com>
To:	Alan Stern <stern@...land.harvard.edu>
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 05/24/2013 03:51 PM, Alan Stern wrote:
>> 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.
> 	 */
ok, I change the comment in the suggested way
> 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).
>
In the USB 2 isochronous the limit is 1024 byte x 3 pkts = 3072, but in 
the code is write 8192. I don't understand why, for the memory page 
size? for have a tolerant limits? for rounding to a nice number?
So I wrote a limit some more big and round, but I agree with you the 
best way is write the correct limit, so I modify in this way, soon.

Federico Manzan

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