linux-kernel - Re: [PATCH] netwinder: nw_gpio_lock is a raw_spinlock

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Message-ID: <1338287087.2536.7.camel@sauron.fi.intel.com>
Date:	Tue, 29 May 2012 13:24:47 +0300
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Christian Dietrich 
	<christian.dietrich@...ormatik.uni-erlangen.de>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.de>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Howells <dhowells@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
	alsa-devel@...a-project.org, vamos-dev@...ts.cs.fau.de
Subject: Re: [PATCH] netwinder: nw_gpio_lock is a raw_spinlock_t

On Tue, 2012-05-29 at 11:11 +0100, David Woodhouse wrote:
> On Tue, 2012-05-29 at 12:06 +0200, Christian Dietrich wrote:
> > Since nw_gpio_lock is a raw_spinlock_t it should be used with the
> > raw_spinlock_* functions and not the spinlock_* variants. Functionally
> > this is equivalent at the moment, because the raw_spinlock_t is the
> > first field of spinlock_t, and therefore &nw_gpio_lock ==
> > &(nw_gpio_lock->rlock). But when other spinlock_t functions use other
> > field they read and write random memory.
> 
> Hm, why are we exposing a raw spinlock to drivers? 
> 
> Should we export a helper function (or macro, I suppose) which does the
> appropriate locking *and* the GPIO operation?

AFAIR, raw spinlock is the one that will not be turned into a
"preemptable" spinlock in the RT tree. E.g., this is needed when dealing
with interrupts. And what if not drivers should use them?

But this commit message did not explain still (although I requested)
_why_ it needs a raw spinlock, which problems it solves?

This URL may be useful for Christian:

http://who-t.blogspot.com/2009/12/on-commit-messages.html

I like that blog-post.

-- 
Best Regards,
Artem Bityutskiy

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