linux-kernel - Re: [PATCH v4 3/4] usb: ffs: check quirk to pad epout buf size when not aligned to maxpacketsize

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Date:	Tue, 5 Nov 2013 15:15:39 +0000
From:	"Cohen, David A" <david.a.cohen@...el.com>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	"balbi@...com" <balbi@...com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/4] usb: ffs: check quirk to pad epout buf size when
 not aligned to maxpacketsize

On 11/05/2013 06:52 AM, Alan Stern wrote:
> On Mon, 4 Nov 2013, David Cohen wrote:
> 
>> Check gadget.quirk_ep_out_aligned_size to decide if buffer size requires
>> to be aligned to maxpacketsize of an out endpoint. ffs_epfile_io() needs
>> to pad epout buffer to match above condition if quirk is found.
>>
>> Signed-off-by: David Cohen <david.a.cohen@...ux.intel.com>
>> ---
>>  drivers/usb/gadget/f_fs.c | 22 ++++++++++++++++++++++
>>  1 file changed, 22 insertions(+)
>>
>> diff --git a/drivers/usb/gadget/f_fs.c b/drivers/usb/gadget/f_fs.c
>> index 75e4b7846a8d..e7c3c3119552 100644
>> --- a/drivers/usb/gadget/f_fs.c
>> +++ b/drivers/usb/gadget/f_fs.c
>> @@ -755,10 +755,13 @@ static ssize_t ffs_epfile_io(struct file *file,
>>  			     char __user *buf, size_t len, int read)
>>  {
>>  	struct ffs_epfile *epfile = file->private_data;
>> +	struct usb_gadget *gadget = epfile->ffs->gadget;
>>  	struct ffs_ep *ep;
>>  	char *data = NULL;
>> +	size_t data_len = 0;
>>  	ssize_t ret;
>>  	int halt;
>> +	size_t orig_len = len;
>>  
>>  	goto first_try;
>>  	do {
>> @@ -794,11 +797,30 @@ first_try:
>>  			goto error;
>>  		}
>>  
>> +		/*
>> +		 * Controller requires buffer size to be aligned to
>> +		 * maxpacketsize of an out endpoint.
>> +		 */
>> +		if (gadget->quirk_ep_out_aligned_size && read) {
>> +			/*
>> +			 * We pass 'orig_len' to usp_ep_align_maxpacketsize()
>> +			 * due to we're in a loop and 'len' may have been
>> +			 * changed.
>> +			 */
>> +			len = usb_ep_align_maxpacketsize(ep->ep, orig_len);
>> +			if (data && len > data_len) {
>> +				kfree(data);
>> +				data = NULL;
>> +				data_len = 0;
>> +			}
>> +		}
> 
> Since the value of orig_len never changes, there's no point calling 
> usb_ep_align_maxpacketsize() inside the loop.  You should call it only 
> once, before the loop starts.  Once you do that, you won't need 
> orig_len at all.

orig_len doesn't change but ep->ep does. If USB specs say max packet
size won't change even if ep does, than we can call it from outside the
loop.

Br, David--
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