Date: Tue, 11 Aug 2015 10:44:06 +0800
From: Jisheng Zhang <jszhang@marvell.com>
To: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
CC: Antoine Tenart <antoine.tenart@free-electrons.com>, <zmxu@marvell.com>,
        <linux-arm-kernel@lists.infradead.org>, <linux-pm@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/3] ARM: berlin: register cpufreq-dt for the BG2Q
Message-ID: <20150811104406.77e0a264@xhacker>
In-Reply-To: <55C90814.3050505@gmail.com>
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	<1438259752-16320-3-git-send-email-antoine.tenart@free-electrons.com>
	<20150731141602.28b28f21@xhacker>	<55C90814.3050505@gmail.com>
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Dear Sebastian,

On Mon, 10 Aug 2015 22:22:44 +0200
Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com> wrote:

> On 31.07.2015 08:16, Jisheng Zhang wrote:
> > On Thu, 30 Jul 2015 14:35:51 +0200
> > Antoine Tenart <antoine.tenart@free-electrons.com> wrote:
> >
> >> The BG2Q SoC uses cpufreq-dt for cpufreq. Register a platform device for
> >> this.
> >>
> >> Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
> >> ---
> [...]
> >> diff --git a/arch/arm/mach-berlin/berlin.c b/arch/arm/mach-berlin/berlin.c
> >> index ac181c6797ee..0de906374994 100644
> >> --- a/arch/arm/mach-berlin/berlin.c
> >> +++ b/arch/arm/mach-berlin/berlin.c
> >> @@ -15,9 +15,21 @@
> [...]
> >> +static void __init berlin_init_late(void)
> >> +{
> >> +	if (of_find_matching_node(NULL, berlin2q_match))
> >> +		platform_device_register_simple("cpufreq-dt", -1, NULL, 0);
> >
> > I'm not sure is it acceptable to always register cpufreq-dt platform device.
> > In cpufreq-dt driver, the probe will exit if there's no cpuclk node.
> 
> Jisheng,
> 
> registering the _device_ without checking for any requirements of
> the _driver_ is usual practice. It it the driver's job to check
> all of them and report an error or warning. So, I am fine with
> adding the device unconditionally.
> 
> Using the .init_late() callback seems reasonable - but can you
> evaluate if we can have cpufreq-dt also for BG2/BG2CD? I'd also
> accept a single, default operating-point.

hmm, if so, we can enable cpufreq-dt for BG2/BG2CD. In fact, there's no any
problem if we don't touch the voltage, only changing the cpufreq should not
introduce stable issues.

> 
> BTW, there is one true point about Jisheng's comment: try to order
> your patches logically correct to avoid unnecessary warnings, i.e.
> 
> 1/3 add cpuclk
> 2/3 add cpufreq-dt properties
> 3/3 register cpufreq-dt device
> 
> If you consider a git-bisect run, you can land in between any of the
> three patches but they are always in the above order - so ordering is
> important.
> 
> Sebastian
> 
> >> +}
> >> +
> >>   static const char * const berlin_dt_compat[] = {
> >>   	"marvell,berlin",
> >>   	NULL,
> >> @@ -25,6 +37,7 @@ static const char * const berlin_dt_compat[] = {
> >>
> >>   DT_MACHINE_START(BERLIN_DT, "Marvell Berlin")
> >>   	.dt_compat	= berlin_dt_compat,
> >> +	.init_late	= berlin_init_late,
> >>   	/*
> >>   	 * with DT probing for L2CCs, berlin_init_machine can be removed.
> >>   	 * Note: 88DE3005 (Armada 1500-mini) uses pl310 l2cc
> >
> 

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