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

[Praveen Talari <quic_ptalari@quicinc.com>]

Hi Dmitry/Bjorn/Krzysztof,

Thank you for review.

On 7/1/2025 4:42 PM, Dmitry Baryshkov wrote:
> On Mon, Jun 30, 2025 at 10:40:25AM +0530, Praveen Talari wrote:
>> 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?
>>>
>>> Seems like this deserves to not be hidden in a middle of a patch series.
>>>
>>>> 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.
>>
>> Introduce PM runtime support to the Qualcomm GENI serial driver to enable
>> better power efficiency and modularity across diverse resource control
>> mechanisms, including Linux and firmware-managed systems.
>>
>> As part of this enhancement, the existing qcom_geni_serial_pm() logic to
>> use standard PM runtime APIs such as pm_runtime_resume_and_get() and
>> pm_runtime_put_sync(). Power state transitions are now handled through
>> the geni_serial_resources_on() and geni_serial_resources_off() functions.
>>
>> Is it fine?
>> Please guide me/correct me if needed
> 
> Please start by stating out the problem that you are trying to solve.
> There is no actual issue description in your patch.

I hope this commit describes the actual problem.

The GENI serial driver currently handles power resource management
through calls to the statically defined geni_serial_resources_on() and
geni_serial_resources_off() functions. This approach reduces modularity
and limits support for platforms with diverse power management 
mechanisms, including resource managed by firmware.

Improve modularity and enable better integration with platform-specific
power management, introduce support for runtime PM. Use
pm_runtime_resume_and_get() and pm_runtime_put_sync() within the
qcom_geni_serial_pm() callback to control resource power state 
transitions based on UART power state changes.

Thanks,
Praveen Talari
> 
>>
>> Thanks,
>> Praveen Talari
>>>
>>> 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@linaro.org>
>>>> Signed-off-by: Praveen Talari <quic_ptalari@quicinc.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?
>>>
>>> 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
>>>>
>