Re: [PATCH] Input: usbtouchscreen - initialize eGalax devices

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Hi Dmitry,

On Fri, Aug 31, 2012 at 04:10:47PM -0700, Dmitry Torokhov wrote:
> On Fri, Aug 31, 2012 at 06:53:53PM -0400, Forest Bond wrote:
> > Hi,
> > 
> > On Fri, Aug 31, 2012 at 04:04:58PM -0400, Alan Stern wrote:
> > > On Fri, 31 Aug 2012, Dmitry Torokhov wrote:
> > > 
> > > > > > +		/* Send a "check active" packet. The response will be read
> > > > > > +		 * later and ignored. */
> > > > > > +		ret = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
> > > > > > +				      0,
> > > > > > +				      USB_DIR_OUT | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
> > > > > > +				      0, 0, "\x0A\x01A", 0,
> > > > > 
> > > > >    You probably can't send data from the .const section (as well as off the
> > > > > stack) -- they can be DMA'ed and there'll be issues with cache consistency on
> > > > > non-x86 arches. You should allocate the data with kmalloc().
> > > > >    Although, on the second thought, maybe I'm wrong in this case... not really
> > > > > sure about sending -- receiving (to the .data section) could certainly be harmful...
> > > > 
> > > > Hmm, do we actually send anything here? The "size" passed to
> > > > usb_control_msg() is 0 so I don't think we use that data at all...
> > > 
> > > Good point.  Perhaps the 0 is a typo, in which case data does get sent
> > > and the buffer must be kmalloc'ed.  If the 0 is correct then the buffer
> > > should be NULL, not "\x0A\x01A" (and what's the purpose of the leading
> > > '0' in the second byte?).
> > > 
> > > In addition, although the bRequestType specifies USB_DIR_OUT, the pipe
> > > value is usb_rcvctrlpipe.  Is this transfer meant to be IN or OUT?
> > 
> > Thanks again to all for the review.  My theory for why the previous patch worked
> > in spite of its wrongness is that the device actually switches modes when it
> > receives a control message with USB_TYPE_VENDOR even though the documentation
> > suggests an actual diagnostic packet must be received.
> > 
> > Does this (untested) patch look more reasonable?
> 
> Yes, but we still need it tested, please.

Great, I'll test it later this evening when I am back in front of the hardware
and follow up with a properly submitted patch.

Thanks again,
Forest
-- 
Forest Bond
http://www.alittletooquiet.net
http://www.rapidrollout.com

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