linux-kernel - Re: [RFC/PATCH 2/2] usb: ffs/dwc3: pad epout buffer size when not aligned to maxpacketsize

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Message-ID: <20131029133724.GH2776@gimli>
Date:	Tue, 29 Oct 2013 08:37:24 -0500
From:	Felipe Balbi <balbi@...com>
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: [RFC/PATCH 2/2] usb: ffs/dwc3: pad epout buffer size when not
 aligned to maxpacketsize

Hi,

On Mon, Oct 28, 2013 at 06:13:00PM -0700, David Cohen wrote:
> DWC3 requires buffer size to be aligned to maxpacketsize of an out
> endpoint. ffs_epfile_io() needs to pad epout buffer to match above
> condition if DWC3 controller is used.
> 
> This patch solves an specific situation but a more generic solution
> should be found.
> 
> Signed-off-by: David Cohen <david.a.cohen@...ux.intel.com>
> ---
>  drivers/usb/gadget/f_fs.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/usb/gadget/f_fs.c b/drivers/usb/gadget/f_fs.c
> index 75e4b78..33880e6 100644
> --- a/drivers/usb/gadget/f_fs.c
> +++ b/drivers/usb/gadget/f_fs.c
> @@ -27,6 +27,7 @@
>  #include <linux/usb/composite.h>
>  #include <linux/usb/functionfs.h>
>  
> +#include "gadget_chips.h"
>  
>  #define FUNCTIONFS_MAGIC	0xa647361 /* Chosen by a honest dice roll ;) */
>  
> @@ -755,10 +756,12 @@ 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;
>  	ssize_t ret;
>  	int halt;
> +	size_t orig_len = len;
>  
>  	goto first_try;
>  	do {
> @@ -794,6 +797,22 @@ first_try:
>  			goto error;
>  		}
>  
> +		/*
> +		 * DWC3 requires buffer size to be aligned to maxpacketsize
> +		 * of an out endpoint.
> +		 * FIXME: a more generic solution might be necessary.
> +		 */

see, gadget drivers shouldn't have to know about DWC3 at all. They need
to know that current UDC has a quirk where EP OUT transactions need to
be aligned to wMaxPacketSize, so what I was expecting to see here was:

		if (test_bit(USB_GADGET_QUIRK_EP_OUT_ALIGNED_SIZE, &gadget->qirks) &&
			!IS_ALIGNED(len, ep->ep->desc->wMaxPacketSize))
			len = align_length(orig_len, wMaxPacketSize);


-- 
balbi

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