linux-kernel - Re: [PATCH RFC RFT 0/3] clk: detect per-user enable imbalances and implement hand-off

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Message-ID: <55DD7C05.6030207@st.com>
Date:	Wed, 26 Aug 2015 10:42:45 +0200
From:	Maxime Coquelin <maxime.coquelin@...com>
To:	Lee Jones <lee.jones@...aro.org>,
	Michael Turquette <mturquette@...libre.com>
CC:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	<linux-kernel@...r.kernel.org>, <linux-clk@...r.kernel.org>,
	<sboyd@...eaurora.org>, <s.hauer@...gutronix.de>,
	<geert@...ux-m68k.org>
Subject: Re: [PATCH RFC RFT 0/3] clk: detect per-user enable imbalances and
 implement hand-off

Hi Lee,

On 08/26/2015 08:54 AM, Lee Jones wrote:
> On Tue, 25 Aug 2015, Michael Turquette wrote:
>
>
>> Maybe I am the one missing something? My goal was to allow the consumer
>> driver to gate the critical clock. So we need clk_disable_unused to
>> actually disable the clock for that to work.
>>
>> I think you are suggesting that clk_disable_unused should *not* disable
>> the clock if it is critical. Can you confirm that?
> My take is that a critical clock should only be disabled when a
> knowledgeable driver wants to gate it for a specific purpose [probably
> using clk_disable()].  Once the aforementioned driver no longer has a
> use for the clock [whether that happens with clk_unprepare_disable()
> or clk_put() ...] the clock should be ungated and be provided with
> critical status once more.
>
How do you differentiate between a knowledgeable and non-knowledgeable 
driver?
Let's take the example of the clock used by the i2c on STi SoCs.
This clock is used by i2c, and is also critical to the system, but only 
i2c takes it.

At first transfer, the i2c will enable the clock and then disables it.

What we would expect here is that the clk_disable does not gate the 
clock, even if only user since the hand-off flag has been set.
Else, system will freeze.

Maxime
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