linux-kernel - Re: [PATCH 2/2] arm: mvebu: Add hardware I/O Coherency support

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Message-ID: <20121024165602.631f070b@skate>
Date:	Wed, 24 Oct 2012 16:56:02 +0200
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Gregory CLEMENT <gregory.clement@...e-electrons.com>
Cc:	Lior Amsalem <alior@...vell.com>, Andrew Lunn <andrew@...n.ch>,
	Ike Pan <ike.pan@...onical.com>,
	Nadav Haklai <nadavh@...vell.com>,
	Ian Molton <ian.molton@...ethink.co.uk>,
	David Marlin <dmarlin@...hat.com>,
	Yehuda Yitschak <yehuday@...vell.com>,
	Jani Monoses <jani.monoses@...onical.com>,
	Russell King <linux@....linux.org.uk>,
	Tawfik Bayouk <tawfik@...vell.com>,
	Dan Frazier <dann.frazier@...onical.com>,
	Eran Ben-Avi <benavi@...vell.com>,
	Leif Lindholm <leif.lindholm@....com>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Jason Cooper <jason@...edaemon.net>,
	Arnd Bergmann <arnd@...db.de>, Jon Masters <jcm@...hat.com>,
	Rob Herring <rob.herring@...xeda.com>,
	Ben Dooks <ben-linux@...ff.org>,
	linux-arm-kernel@...ts.infradead.org,
	Chris Van Hoof <vanhoof@...onical.com>,
	Nicolas Pitre <nico@...xnic.net>, linux-kernel@...r.kernel.org,
	Maen Suleiman <maen@...vell.com>,
	Shadi Ammouri <shadi@...vell.com>,
	Olof Johansson <olof@...om.net>
Subject: Re: [PATCH 2/2] arm: mvebu: Add hardware I/O Coherency support

Dear Gregory CLEMENT,

On Wed, 24 Oct 2012 16:39:13 +0200, Gregory CLEMENT wrote:

> > As others said, the prefix is wrong. Since the file is named coherency,
> > maybe just "coherency_" as the prefix? Not sure, though. Shouldn't the
> > file be named coherency-armada-370-xp.c, as we have done for the irq
> > controller file? In that case, the armada_370_xp prefix would make
> > sense
> 
> I would prefer to just use coherency_ everywhere and keep the name of
> the file as is. It made sense to suffix the irq file with
> armada-370-xp because the other mvebu SoCs have their own irq
> controller. Whereas, as far as I know the coherency unit is only
> present in the Armada 370/XP.

Well your argumentation may also be seen as an argument to name it
coherency-armada-370-xp.c :-) I don't have a strong opinion on this
though, and we can always rename it later if needed.

> >>  int armada_xp_get_cpu_count(void)
> >>  {
> >>  	int reg, cnt;
> > 
> > static?
> 
> Which function?
> armada_xp_get_cpu_count and armada_370_xp_set_cpu_coherent are exported
> and moreover are not part of this patch set but the SMP one.

Ok, then maybe this function shouldn't be between the DMA operations
implementation and the bus notifier callback.

> Yes indeed code in headsmp.S and armada_xp_smp_prepare_cpus() are
> redundant we can simplify it. I will change it in the SMP series and
> for this series also.

Great, thanks!

> > Do we have a good reason for having
> > armada_370_xp_coherency_iocache_init() separate from
> > armada_370_xp_coherency_iocache_init() ? I.e, what prevents us from
> 
> No good reason because they are the same! ;)

Oops, indeed. but I see that you fixed the problem.

> But more seriously, armada_370_xp_coherency_init() is called as an
> early_init call whereas armada_370_xp_coherency_iocache_init() is called
> later by armada_370_xp_dt_init(). I have to check if we can use
> bus_register_notifier() from an early_init call or if we still need to
> call armada_370_xp_coherency_init() as an early_init call.

The early_initcall() is mandatory, see the comment on top of it:

+/* Coherency initialization have to be done before the SMP
+ * initialization of the CPUs*/
+early_initcall(armada_370_xp_coherency_init);

(BTW, there is a missing space between CPUs and the comment terminator).

So, my point was more: is it possible to register the bus notifier
as early as inside an early_initcall() callback.

Best regards,

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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