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

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

[Marek Vasut]

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");
 			return ret;
-- 
2.45.2

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

[Alain Volmat]

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
> 

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

[Marek Vasut]

On 9/30/24 8:38 PM, Alain Volmat wrote:
> Hi Marek,

Hello Alain,

> 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>
Fixed in V2, thanks !