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

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:

quoted

Hi,

On Fri, Aug 31, 2012 at 04:04:58PM -0400, Alan Stern wrote:

quoted

On Fri, 31 Aug 2012, Dmitry Torokhov wrote:

quoted

quoted

quoted

+		/* 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