linux-kernel - Re: [PATCH v6 7/8] serial: qcom-geni: Enable PM runtime for serial driver

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Message-ID: <ed381bb7-dfc8-4a27-b044-11deb7e75a81@quicinc.com>
Date: Fri, 20 Jun 2025 15:04:15 +0530
From: Praveen Talari <quic_ptalari@...cinc.com>
To: Bjorn Andersson <andersson@...nel.org>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby
	<jirislaby@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski
	<krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Konrad Dybcio
	<konradybcio@...nel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-serial@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <psodagud@...cinc.com>, <djaggi@...cinc.com>,
        <quic_msavaliy@...cinc.com>, <quic_vtanuku@...cinc.com>,
        <quic_arandive@...cinc.com>, <quic_mnaresh@...cinc.com>,
        <quic_shazhuss@...cinc.com>
Subject: Re: [PATCH v6 7/8] serial: qcom-geni: Enable PM runtime for serial
 driver

Hi Bjorn,

Thank you for review.

On 6/17/2025 9:23 PM, Bjorn Andersson wrote:
> On Fri, Jun 06, 2025 at 10:51:13PM +0530, Praveen Talari wrote:
>> Add Power Management (PM) runtime support to Qualcomm GENI
>> serial driver.
>>
> 
> Doesn't this have impact on the behavior outside of your
> project? Or is the transition from qcom_geni_serial_pm() to explicit
> RPM merely moving code around?
There is no impact on functionality and behavior with this change.

The transition is purely refactor.

Using PM runtime APIs such as
pm_runtime_resume_and_get() and pm_runtime_put_sync() to manage resource 
both locally and firmware.

> 
> Seems like this deserves to not be hidden in a middle of a patch series.
This depends on refactored patches.
> 
>> Introduce necessary callbacks and updates to ensure seamless
>> transitions between power states, enhancing overall power
>> efficiency.
>>
> 
> This commit message fails to state why we need runtime PM support in the
> driver.
Sure, will update commit text.
> 
> Also, start your commit message with a problem description, per
> https://docs.kernel.org/process/submitting-patches.html#describe-your-changes
> 
>> Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
>> Signed-off-by: Praveen Talari <quic_ptalari@...cinc.com>
>> ---
>> v5 -> v6
>> - added reviewed-by tag in commit
>> - added __maybe_unused to PM callback functions to avoid
>>    warnings of defined but not used
>> ---
>>   drivers/tty/serial/qcom_geni_serial.c | 33 +++++++++++++++++++++++----
>>   1 file changed, 29 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
>> index b6fa7dc9b1fb..3691340ce7e8 100644
>> --- a/drivers/tty/serial/qcom_geni_serial.c
>> +++ b/drivers/tty/serial/qcom_geni_serial.c
>> @@ -1686,10 +1686,10 @@ static void qcom_geni_serial_pm(struct uart_port *uport,
>>   		old_state = UART_PM_STATE_OFF;
>>   
>>   	if (new_state == UART_PM_STATE_ON && old_state == UART_PM_STATE_OFF)
>> -		geni_serial_resources_on(uport);
>> +		pm_runtime_resume_and_get(uport->dev);
>>   	else if (new_state == UART_PM_STATE_OFF &&
>>   		 old_state == UART_PM_STATE_ON)
>> -		geni_serial_resources_off(uport);
>> +		pm_runtime_put_sync(uport->dev);
>>   
>>   }
>>   
>> @@ -1827,9 +1827,11 @@ static int qcom_geni_serial_probe(struct platform_device *pdev)
>>   		return ret;
>>   	}
>>   
>> +	pm_runtime_enable(port->se.dev);
> 
> Any reason not to use devm_pm_runtime_enable() and avoid the
> two pm_runtime_disable() below?

I agree, will update in next patch-set.
> 
> Regards,
> Bjorn
> 
>> +
>>   	ret = uart_add_one_port(drv, uport);
>>   	if (ret)
>> -		return ret;
>> +		goto error;
>>   
>>   	if (port->wakeup_irq > 0) {
>>   		device_init_wakeup(&pdev->dev, true);
>> @@ -1839,11 +1841,15 @@ static int qcom_geni_serial_probe(struct platform_device *pdev)
>>   			device_init_wakeup(&pdev->dev, false);
>>   			ida_free(&port_ida, uport->line);
>>   			uart_remove_one_port(drv, uport);
>> -			return ret;
>> +			goto error;
>>   		}
>>   	}
>>   
>>   	return 0;
>> +
>> +error:
>> +	pm_runtime_disable(port->se.dev);
>> +	return ret;
>>   }
>>   
>>   static void qcom_geni_serial_remove(struct platform_device *pdev)
>> @@ -1855,9 +1861,26 @@ static void qcom_geni_serial_remove(struct platform_device *pdev)
>>   	dev_pm_clear_wake_irq(&pdev->dev);
>>   	device_init_wakeup(&pdev->dev, false);
>>   	ida_free(&port_ida, uport->line);
>> +	pm_runtime_disable(port->se.dev);
>>   	uart_remove_one_port(drv, &port->uport);
>>   }
>>   
>> +static int __maybe_unused qcom_geni_serial_runtime_suspend(struct device *dev)
>> +{
>> +	struct qcom_geni_serial_port *port = dev_get_drvdata(dev);
>> +	struct uart_port *uport = &port->uport;
>> +
>> +	return geni_serial_resources_off(uport);
>> +}
>> +
>> +static int __maybe_unused qcom_geni_serial_runtime_resume(struct device *dev)
>> +{
>> +	struct qcom_geni_serial_port *port = dev_get_drvdata(dev);
>> +	struct uart_port *uport = &port->uport;
>> +
>> +	return geni_serial_resources_on(uport);
>> +}
>> +
>>   static int qcom_geni_serial_suspend(struct device *dev)
>>   {
>>   	struct qcom_geni_serial_port *port = dev_get_drvdata(dev);
>> @@ -1901,6 +1924,8 @@ static const struct qcom_geni_device_data qcom_geni_uart_data = {
>>   };
>>   
>>   static const struct dev_pm_ops qcom_geni_serial_pm_ops = {
>> +	SET_RUNTIME_PM_OPS(qcom_geni_serial_runtime_suspend,
>> +			   qcom_geni_serial_runtime_resume, NULL)
>>   	SYSTEM_SLEEP_PM_OPS(qcom_geni_serial_suspend, qcom_geni_serial_resume)
>>   };
>>   
>> -- 
>> 2.17.1
>>