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 09:52:54 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	David Cohen <david.a.cohen@...ux.intel.com>
cc:	balbi@...com, <gregkh@...uxfoundation.org>,
	<linux-usb@...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 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.

Alan Stern

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