linux-kernel - Re: [PATCH v2 1/6] hid: new driver for PicoLCD device

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Message-ID: <20100322043508.GC31621@core.coreip.homeip.net>
Date:	Sun, 21 Mar 2010 21:35:09 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Bruno Prémont <bonbons@...ux-vserver.org>
Cc:	Jiri Kosina <jkosina@...e.cz>, linux-input@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-fbdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Rick L. Vinyard Jr." <rvinyard@...nmsu.edu>,
	Nicu Pavel <npavel@...ner.com>,
	Oliver Neukum <oliver@...kum.org>,
	Jaya Kumar <jayakumar.lkml@...il.com>
Subject: Re: [PATCH v2 1/6] hid: new driver for PicoLCD device

On Sun, Mar 21, 2010 at 05:37:37PM +0100, Bruno Prémont wrote:
> On Sat, 20 March 2010 Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:
> > > +	usbhid_submit_report(data->hdev, report, USB_DIR_OUT);
> > > +	complete_all(&data->ready);
> > > +	INIT_COMPLETION(data->ready);
> > 
> > Umm, what does this do, exactly?
> 
> It wakes up anyone waiting on the completion and then resets the completion
> as otherwise any future attempt to wait on it would succeed immediately.
> 

You realize that if you re-initialize the completion right after
signalling it there is a big chance the waiters will miss it (they do
check completion->done flags that you reset right away.

In general completions are suited for something that happens once (a
single request - allocated - processed - signalled) but not for
repeating use.

Thanks.

-- 
Dmitry
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