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

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Date:   Wed, 16 May 2018 10:15:28 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Oleksandr Andrushchenko <andr2000@...il.com>
Cc:     xen-devel@...ts.xenproject.org, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org, jgross@...e.com, lyan@...e.com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        andrii_chepurnyi@...m.com,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
Subject: Re: [PATCH v3 2/2] Input: xen-kbdfront - allow better run-time
 configuration

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;

?

Thanks.

-- 
Dmitry