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

From: Maxime Coquelin
Date: Wed Aug 26 2015 - 04:43:16 EST

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.

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