linux-kernel - Re: [PATCH] clk: samsung: exynos7: Enable clocks for CMU_CCORE and CMU

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Message-id: <570E2123.1000107@samsung.com>
Date:	Wed, 13 Apr 2016 12:36:19 +0200
From:	Sylwester Nawrocki <s.nawrocki@...sung.com>
To:	Tomasz Figa <tomasz.figa@...il.com>,
	Alim Akhtar <alim.akhtar@...sung.com>
Cc:	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Thomas Abraham <thomas.ab@...sung.com>,
	Krzysztof Kozłowski <k.kozlowski@...sung.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>, linux-clk@...r.kernel.org,
	Stephen Boyd <sboyd@...eaurora.org>,
	Michael Turquette <mturquette@...libre.com>
Subject: Re: [PATCH] clk: samsung: exynos7: Enable clocks for CMU_CCORE and
 CMU_FSYS0 blocks

On 04/13/2016 08:26 AM, Tomasz Figa wrote:
>> > @@ -205,7 +206,11 @@ static struct samsung_cmu_info topc_cmu_info __initdata = {
>> >
>> >  static void __init exynos7_clk_topc_init(struct device_node *np)
>> >  {
>> > +       struct clk *clk;
>> > +
>> >         samsung_cmu_register_one(np, &topc_cmu_info);
>> > +       clk = __clk_lookup("aclk_ccore_133");
>> > +       clk_prepare_enable(clk);
>
> Shouldn't this be rather done before calling
> samsung_cmu_register_one()? I don't remember exactly, but wouldn't
> clock registration trigger reading back current (mux, div) values from
> registers?
> 
> Also, do we have any guarantees on order of initialization of
> particular CMUs? I believe this will happen in order of DT nodes and
> so would be not any kind of guarantee at all.

If these clocks need to be kept enabled perhaps it's better to just set
CLK_IS_CRITICAL flag for them? Patches adding this flag are already in
clk-next branch in the clk git tree. This way the clocks would get 
enabled within the clk_register() call.

The CMU registration order is enforced by listing input clocks to each
CMU in DT. However, I wouldn't be concerned much about it in context 
of this patch. We are enabling here clocks which belong to same CMU.
samsung_cmu_register_one() needs to be called first for subsequent 
__clk_lookup() calls to work.

Perhaps related bits need to be set manually in CMU registers before
registering a clock provider for the CMU, to fulfil the requirements.

Anyway, summary of the $subject patch seems not precise enough:

"This patch enables clocks for CMU_CCORE and CMU_FSYS0 blocks. This is
required before accessing registers of these blocks."

We need to enable selected clocks (i.e. access the CMU's registers)
before accessing this CMU's registers? 

--
Regards, 
Sylwester