linux-kernel - Re: [PATCH] input: Synaptics USB device driver

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Message-ID: <20120105060138.704cfb16@greyhound>
Date:	Thu, 5 Jan 2012 06:01:38 +0000
From:	Jan Steinhoff <mail@...-steinhoff.de>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Oliver Neukum <oneukum@...e.de>, Jiri Kosina <jkosina@...e.cz>,
	Alessandro Rubini <rubini@...vis.unipv.it>,
	linux-input@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] input: Synaptics USB device driver

On Wed, 4 Jan 2012 02:05:53 -0800
Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:
> On Wed, Jan 04, 2012 at 10:56:20AM +0100, Oliver Neukum wrote:
> > Am Mittwoch, 4. Januar 2012, 10:41:03 schrieb Dmitry Torokhov:
> > > +static int synusb_probe(struct usb_interface *intf,
> > > +			const struct usb_device_id *id)
> > > +{
[...]
> > > +	synusb->urb = usb_alloc_urb(0, GFP_KERNEL);
> > > +	if (!synusb->urb) {
> > > +		error = -ENOMEM;
> > > +		goto err_free_mem;
> > > +	}
> > > +
> > > +	synusb->data = usb_alloc_coherent(udev,
> > > SYNUSB_RECV_SIZE, GFP_KERNEL,
> > > +
> > > &synusb->urb->transfer_dma);
> > > +	if (!synusb->data) {
> > > +		error = -ENOMEM;
> > > +		goto err_free_urb;
> > > +	}
> > > +
> > > +	usb_fill_int_urb(synusb->urb, udev,
> > > +			 usb_rcvintpipe(udev,
> > > ep->bEndpointAddress),
> > > +			 synusb->data, SYNUSB_RECV_SIZE,
> > > +			 synusb_irq, synusb,
> > > +			 ep->bInterval);
> > > +	synusb->urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
> > 
> > According to the comment in the original driver you must submit the
> > URB. Are you sure not doing so is save?
> 
> Seems to work here...

Let me comment on this issue in more detail, so you can better judge
what is the "right" solution here.

Both ways actually work. But, at least for the cPad, the device will
pretend it got reconnected if the int urb is not fetched (while not
suspended, of course). This means it would disconnect if no input device
is opened (AFAIK most X.org input drivers close the devices when one
switches to console) and one touches the pad (actually, a slight breeze
of air might be enough, it is very sensitive!). Another annoying side
effect in the case of the cPad is that the background light flashes on
every reconnect.
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