linux-kernel - Re: [PATCH 1/1] Input: joydev - fix axes values sent in initial js

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Date:	Wed, 12 Sep 2012 21:52:06 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Vojtěch Boček <vbocek@...il.com>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] Input: joydev - fix axes values sent in initial
 js_event

On Wed, Sep 05, 2012 at 10:09:57PM +0200, Vojtěch Boček wrote:
> Hi,
> 
> 2012/9/5 Dmitry Torokhov <dmitry.torokhov@...il.com>
> > So what guarantees that joystick events will arrive in time, before
> > joydev_generate_startup_event() is called? It looks like your solution
> > is racy...
> >
> > I wonder if we should not generate the startup event until we have seen
> > at least one EV_SYN, i.e. entire device state has been transmitted to
> > us.
> 
> I just tried to delay read() until first EV_SYN arrives as you suggested,
> but that was not the problem, at least not the main one. First joystick
> input events arrives immediately after it is plugged in and driver is loaded,
> but when that happens, joydev may not be (and most likely is not)
> opened yet, which means the events will never reach joydev because of
> "if (!handle->open)" check in input_pass_event.
> 
> I wonder how to handle this. Is "if(!handle->open)" valid check? I think so,
> my guess is that joydev is the only handler with internal buffer, and it
> is useless to update that buffer when the device is not opened.
> I think reloading abs values on joydev open should be okay.
> 
> I suppose that if we reload abs values on joydev open, waiting for first
> sync is not needed, yes?
> 
> So the patch could look like this:

This makes sense. Just to confirm - have you tried the patch and
verified it works for you?

Thanks.

-- 
Dmitry
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