Re: [Xen-devel] [PATCH v3 2/2] Input: xen-kbdfront - allow better run-time configuration

[Oleksandr Andrushchenko <andr2000@xxxxxxxxx>]

On 05/16/2018 08:15 PM, Dmitry Torokhov wrote:
> Hi Oleksandr,
>
> On Mon, May 14, 2018 at 05:40:29PM +0300, Oleksandr Andrushchenko wrote:
> > @@ -211,93 +220,114 @@ static int xenkbd_probe(struct xenbus_device *dev,
> >         if (!info->page)
> >                 goto error_nomem;
> >   
> > -	/* Set input abs params to match backend screen res */
> > -       abs = xenbus_read_unsigned(dev->otherend,
> > -                                  XENKBD_FIELD_FEAT_ABS_POINTER, 0);
> > -       ptr_size[KPARAM_X] = xenbus_read_unsigned(dev->otherend,
> > -                                                 XENKBD_FIELD_WIDTH,
> > -                                                 ptr_size[KPARAM_X]);
> > -       ptr_size[KPARAM_Y] = xenbus_read_unsigned(dev->otherend,
> > -                                                 XENKBD_FIELD_HEIGHT,
> > -                                                 ptr_size[KPARAM_Y]);
> > -       if (abs) {
> > -               ret = xenbus_write(XBT_NIL, dev->nodename,
> > -                                  XENKBD_FIELD_REQ_ABS_POINTER, "1");
> > -               if (ret) {
> > -                       pr_warn("xenkbd: can't request abs-pointer\n");
> > -                       abs = 0;
> > -               }
> > -       }
> > +       /*
> > +        * The below are reverse logic, e.g. if the feature is set, then
> > +        * do not expose the corresponding virtual device.
> > +        */
> > +       with_kbd = !xenbus_read_unsigned(dev->nodename,
> > +                                        XENKBD_FIELD_FEAT_DSBL_KEYBRD, 0);
> >   
> > -	touch = xenbus_read_unsigned(dev->nodename,
> > -                                    XENKBD_FIELD_FEAT_MTOUCH, 0);
> > -       if (touch) {
> > +       with_ptr = !xenbus_read_unsigned(dev->nodename,
> > +                                        XENKBD_FIELD_FEAT_DSBL_POINTER, 0);
> > +
> > +       /* Direct logic: if set, then create multi-touch device. */
> > +       with_mtouch = xenbus_read_unsigned(dev->nodename,
> > +                                          XENKBD_FIELD_FEAT_MTOUCH, 0);
> > +       if (with_mtouch) {
> >                 ret = xenbus_write(XBT_NIL, dev->nodename,
> >                                    XENKBD_FIELD_REQ_MTOUCH, "1");
> >                 if (ret) {
> >                         pr_warn("xenkbd: can't request multi-touch");
> > -                       touch = 0;
> > +                       with_mtouch = 0;
> >                 }
> >         }
> Does it make sense to still end up calling xenkbd_connect_backend() when
> all interfaces (keyboard, pointer, and multitouch) are disabled? Should
> we do:
>
>         if (!(with_kbd || || with_ptr || with_mtouch))
>                 return -ENXIO;
>
> ?
It does make sense. Then we probably need to move all xenbus_read_unsigned
calls to the very beginning of the .probe, so no memory allocations are made
which will be useless if we return -ENXIO, e.g. something like

static int xenkbd_probe(struct xenbus_device *dev,
                  const struct xenbus_device_id *id)
{
    int ret, i;
    bool with_mtouch, with_kbd, with_ptr;
    struct xenkbd_info *info;
    struct input_dev *kbd, *ptr, *mtouch;

<read with_mtouch, with_kbd, with_ptr here>

if (!(with_kbd | with_ptr | with_mtouch))
        return -ENXIO;

Does the above looks ok?
> Thanks.
Thank you,
Oleksandr

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