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

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Date:   Thu, 17 May 2018 08:31:54 +0300
From:   Oleksandr Andrushchenko <andr2000@...il.com>
To:     Dmitry Torokhov <dmitry.torokhov@...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

On 05/17/2018 12:08 AM, Dmitry Torokhov wrote:
> On Wed, May 16, 2018 at 08:47:30PM +0300, Oleksandr Andrushchenko wrote:
>> 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?
> Yes. Another option is to keep the check where I suggested and do
>
> 	if (...) {
> 		ret = -ENXIO;
> 		goto error;
> 	}
>
> Whichever you prefer is fine with me.
I will go with the change you suggested and
I'll send v4 tomorrow then.
> Thanks.
>
Thank you,
Oleksandr