linux-kernel - Re: [PATCH 1/1] Staging: hv: mousevsc: Move the mouse driver out of staging

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Message-ID: <20111027043120.GA15725@core.coreip.homeip.net>
Date:	Wed, 26 Oct 2011 21:31:20 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	KY Srinivasan <kys@...rosoft.com>
Cc:	"gregkh@...e.de" <gregkh@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"virtualization@...ts.osdl.org" <virtualization@...ts.osdl.org>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Jiri Kosina <jkosina@...e.cz>
Subject: Re: [PATCH 1/1] Staging: hv: mousevsc: Move the mouse driver out of
 staging

On Thu, Oct 27, 2011 at 01:19:50AM +0000, KY Srinivasan wrote:
> 
> 
> > -----Original Message-----
> > From: Dmitry Torokhov [mailto:dmitry.torokhov@...il.com]
> > Sent: Wednesday, October 26, 2011 8:09 PM
> > To: KY Srinivasan
> > Cc: gregkh@...e.de; linux-kernel@...r.kernel.org;
> > devel@...uxdriverproject.org; virtualization@...ts.osdl.org; linux-
> > input@...r.kernel.org; Haiyang Zhang; Jiri Kosina
> > Subject: Re: [PATCH 1/1] Staging: hv: mousevsc: Move the mouse driver out of
> > staging
> > 
> > On Sun, Oct 23, 2011 at 03:45:14PM +0000, KY Srinivasan wrote:
> > > > > +
> > > > > +	t = wait_for_completion_timeout(&input_dev->wait_event, 5*HZ);
> > > > > +	if (t == 0) {
> > > > > +		ret = -ETIMEDOUT;
> > > > > +		goto cleanup;
> > > > > +	}
> > > > > +
> > > > > +	response = &input_dev->protocol_resp;
> > > > > +
> > > > > +	if (!response->response.approved) {
> > > > > +		pr_err("synthhid protocol request failed (version %d)",
> > > > > +		       SYNTHHID_INPUT_VERSION);
> > > > > +		ret = -ENODEV;
> > > > > +		goto cleanup;
> > > > > +	}
> > > > > +
> > > > > +	t = wait_for_completion_timeout(&input_dev->wait_event, 5*HZ);
> > > >
> > > > We just completed the wait for this completion, why are we waiting on
> > > > the same completion again?
> > >
> > > In response to our initial query, we expect the host to respond back with two
> > > distinct pieces of information; we wait for both these responses.
> > 
> > I think you misunderstand how completion works in Linux. IIRC about
> > Windows events they are different ;) You can not signal completion
> > several times and then expect to wait corrsponding number of times. Once
> > you signal completion is it, well, complete.
> 
> Looking at the code for complete(), it looks like the "done" state is incremented
> each time complete() is invoked and  the  code for do_wait_for_common() decrements the 
> done state each time it is invoked (if the completion is properly signaled and we are not dealing
> with a timeout. So, what am I missing here.

Hmm, you are right. I am not sure why I thought that completion has to
be re-initialized before it can be reused... I guess this is true only
if one uses complete_all().

-- 
Dmitry
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