From mboxrd@z Thu Jan  1 00:00:00 1970
From: Oliver Neukum <oneukum@suse.de>
Subject: Re: [PATCH] HID: sony: Enable Gasia third-party PS3 controllers
Date: Tue, 10 Feb 2015 09:14:36 +0100
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To: Lauri Kasanen <cand@gmx.com>
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On Mon, 2015-02-09 at 20:44 +0200, Lauri Kasanen wrote:
> On Mon, 09 Feb 2015 11:08:01 +0100
> Oliver Neukum <oneukum@suse.de> wrote:
> 
> > > +	ret = usb_interrupt_msg(dev, usb_sndintpipe(dev, 0x02),
> > > +				buf2, sizeof(buf2),
> > > +				&transfered, USB_CTRL_SET_TIMEOUT);
> > 
> > You cannot do this. Even for a single byte DMA on the stack is
> > wrong. Not on all architectures it works at all and you violate
> > the DMA constrainsts. You must use kmalloc().
> 
> Hi Oliver,
> 
> Does this still apply when using hid_hw_output_report?

Yes. For USB devices hid_hw_output_report() goes to
usbhid_output_report(). That goes to usb_interrupt_msg(),
which passes the buffer pointer. It will then be mapped
for DMA. You must not do that on the stack.

	HTH
		Oliver