Re: usbtouchscreen: version 0.4

[Daniel Ritz <daniel.ritz-ml@swissonline.ch>]

Hi Dan

On 2015-06-06 18:52 , Dan Carpenter wrote:
> Hi Daniel,
>
> I had a question about patch 5d8926658ce4: "usbtouchscreen: version 0.4"
> from Jul 31, 2006.
That's ancient :)
>
> drivers/input/touchscreen/usbtouchscreen.c
>   1326  static void usbtouch_process_multi(struct usbtouch_usb *usbtouch,
>   1327                                     unsigned char *pkt, int len)
>   1328  {
>   1329          unsigned char *buffer;
>   1330          int pkt_len, pos, buf_len, tmp;
>   1331  
>   1332          /* process buffer */
>   1333          if (unlikely(usbtouch->buf_len)) {
>   1334                  /* try to get size */
>   1335                  pkt_len = usbtouch->type->get_pkt_len(
>   1336                                  usbtouch->buffer, usbtouch->buf_len);
>
> ->get_pkt_len() returns -1 on error.

No, it doesn't and never has. In 62aa366d9b015 I added a bit of documentation:

/*
 * used to get the packet len. possible return values:
 * > 0: packet len
 * = 0: skip one byte
 * < 0: -return value more bytes needed
 */
int (*get_pkt_len) (unsigned char *pkt, int len);

So -1 means "need one more byte for a complete data packet". That byte will be
in delivered in the next invocation of usbtouch_irq(). One "touchscreen data packet"
can be split across multiple "usb packets" for some devices.

regards
-Daniel