Re: usb : mass storage : short_not_ok for non usb3 udc

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Thu, 26 Jul 2012, Felipe Balbi wrote:

> Hi,
> 
> On Wed, Jul 25, 2012 at 02:53:00PM +0200, Rajaram REGUPATHY wrote:
> > The short_not_ok field is used by class drivers to indicate udc whether short packet is expected during a particular transfer.
> > In case of mass storage, during command and status phase this field is set as false and set to true during data phase.
> > musb driver uses this field to decide whether to program DMA for mode1.
> > This code is essential for musb driver to program DMA.
> > 
> > Signed-off-by: Balakumar Rajendran <balakumar.rajendran@xxxxxxxxxxxxxx>
> > Signed-off-by: Rajaram R <ragupathy.rajaram@xxxxxxxxxxxxxx>
> > ---
> >  drivers/usb/gadget/f_mass_storage.c |    9 +++++++++
> >  1 files changed, 9 insertions(+), 0 deletions(-)
> > 
> > diff --git a/drivers/usb/gadget/f_mass_storage.c b/drivers/usb/gadget/f_mass_storage.c
> > index f67b453..db8bf4a 100644
> > --- a/drivers/usb/gadget/f_mass_storage.c
> > +++ b/drivers/usb/gadget/f_mass_storage.c
> > @@ -878,6 +878,7 @@ static int do_write(struct fsg_common *common)
> >  	unsigned int		amount;
> >  	ssize_t			nwritten;
> >  	int			rc;
> > +	struct usb_gadget *gadget = common->cdev->gadget;
> >  
> >  	if (curlun->ro) {
> >  		curlun->sense_data = SS_WRITE_PROTECTED; @@ -960,6 +961,8 @@ static int do_write(struct fsg_common *common)
> >  			 * the bulk-out maxpacket size.
> >  			 */
> >  			set_bulk_out_req_length(common, bh, amount);
> > +			if (!gadget_is_superspeed(gadget))
> > +				bh->outreq->short_not_ok = 1;
> 
> I'm not sure if this entirely correct. We are now setting req->length
> aligned to wMaxPacketSize, which means that if we're to receive CBW of
> 31 bytes, req->length will be set to 512. In this case a short packet
> _is_ ok. It's the only way for us to know that the transfer has ended.

It's okay.  This particular section of code applies only to the data
phase of a transfer.  The CBW is sent in the command phase, and there
the patch sets short_not_ok to 0.

Alan Stern

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