linux-kernel - Re: [PATCH 1/2] i2c: designware: Fix clock issue when PM is disabled

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Message-ID: <e884f5c2-0bb3-42a2-9d96-d199e60f1dec@socionext.com>
Date: Thu, 24 Jul 2025 13:05:48 +0900
From: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To: Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Mika Westerberg <mika.westerberg@...ux.intel.com>,
 Jan Dabros <jsd@...ihalf.com>, Andi Shyti <andi.shyti@...nel.org>
Cc: linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
 ito.kohei@...ionext.com
Subject: Re: [PATCH 1/2] i2c: designware: Fix clock issue when PM is disabled

On 2025/07/24 11:13, Kunihiko Hayashi wrote:
> When removing the driver, enable the clocks once by calling
> pm_runtime_get_sync(), and call pm_runtime_put_sync() to disable
> the clocks.
> 
> If CONFIG_PM=y, clocks for this controller are disabled when it's in
> the idle state. So the clocks are properly disabled when the driver
> exits.
> 
> Othewise, the clocks are always enabled and the PM functions have
> no effect. Therefore, the driver exits without disabling the clocks.
> 
>      # cat /sys/kernel/debug/clk/clk-pclk/clk_enable_count
>      18
>      # echo 1214a000.i2c > /sys/bus/platform/drivers/i2c_designware/bind
>      # cat /sys/kernel/debug/clk/clk-pclk/clk_enable_count
>      20
>      # echo 1214a000.i2c > /sys/bus/platform/drivers/i2c_designware/unbind
>      # cat /sys/kernel/debug/clk/clk-pclk/clk_enable_count
>      20
> 
> To ensure that the clocks can be disabled correctly even without
> CONFIG_PM=y, should add the following fixes:
> 
> - Replace with pm_runtime_put_noidle(), which only decrements the clock
>    count.

This description is wrong.
The pm_runtime_put_noidle() decrements the runtime PM usage count.

> - Call i2c_dw_prepare_clk(false) to explicitly disable the clocks.

This decrements the clock count.

I'll fix it and resend as v2.

Thanks,

---
Best Regards
Kunihiko Hayashi