Re: [PATCH] i2c: stm32f7: Do not prepare/unprepare clock during runtime suspend/resume

[Alain Volmat <alain.volmat@foss.st.com>]

Hi Marek,

thanks a lot for the patch.

On Sat, Sep 28, 2024 at 03:43:46AM +0200, Marek Vasut wrote:
> In case there is any sort of clock controller attached to this I2C bus
> controller, for example Versaclock or even an AIC32x4 I2C codec, then
> an I2C transfer triggered from the clock controller clk_ops .prepare
> callback may trigger a deadlock on drivers/clk/clk.c prepare_lock mutex.
> 
> This is because the clock controller first grabs the prepare_lock mutex
> and then performs the prepare operation, including its I2C access. The
> I2C access resumes this I2C bus controller via .runtime_resume callback,
> which calls clk_prepare_enable(), which attempts to grab the prepare_lock
> mutex again and deadlocks.
> 
> Since the clock are already prepared since probe() and unprepared in
> remove(), use simple clk_enable()/clk_disable() calls to enable and
> disable the clock on runtime suspend and resume, to avoid hitting the
> prepare_lock mutex.
> 
> Signed-off-by: Marek Vasut <marex@denx.de>
> ---
> Cc: Alain Volmat <alain.volmat@foss.st.com>
> Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
> Cc: Andi Shyti <andi.shyti@kernel.org>
> Cc: Christoph Niedermaier <cniedermaier@dh-electronics.com>
> Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
> Cc: Pierre-Yves MORDRET <pierre-yves.mordret@foss.st.com>
> Cc: kernel@dh-electronics.com
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-i2c@vger.kernel.org
> Cc: linux-stm32@st-md-mailman.stormreply.com
> ---
>  drivers/i2c/busses/i2c-stm32f7.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-stm32f7.c b/drivers/i2c/busses/i2c-stm32f7.c
> index cfee2d9c09de3..65c035728a4fa 100644
> --- a/drivers/i2c/busses/i2c-stm32f7.c
> +++ b/drivers/i2c/busses/i2c-stm32f7.c
> @@ -2395,7 +2395,7 @@ static int __maybe_unused stm32f7_i2c_runtime_suspend(struct device *dev)
>  	struct stm32f7_i2c_dev *i2c_dev = dev_get_drvdata(dev);
>  
>  	if (!stm32f7_i2c_is_slave_registered(i2c_dev))
> -		clk_disable_unprepare(i2c_dev->clk);
> +		clk_disable(i2c_dev->clk);
>  
>  	return 0;
>  }
> @@ -2406,7 +2406,7 @@ static int __maybe_unused stm32f7_i2c_runtime_resume(struct device *dev)
>  	int ret;
>  
>  	if (!stm32f7_i2c_is_slave_registered(i2c_dev)) {
> -		ret = clk_prepare_enable(i2c_dev->clk);
> +		ret = clk_enable(i2c_dev->clk);
>  		if (ret) {
>  			dev_err(dev, "failed to prepare_enable clock\n");

The call now being clk_enable, could you also change the error message
from prepare_enable to enable ?

With that done,
Acked-by: Alain Volmat <alain.volmat@foss.st.com>

Regards,
Alain

>  			return ret;
> -- 
> 2.45.2
>