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

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Message-ID: <tt2crsexdnhlotlo3z5uxyta6jrnnvom7aqwsjvopwueazbuih@2l4h6xjpwlar>
Date: Tue, 1 Jul 2025 14:12:07 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Praveen Talari <quic_ptalari@...cinc.com>
Cc: Bjorn Andersson <andersson@...nel.org>,
        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

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.

> 
> 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@...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?
> > 
> > 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
> > > 

-- 
With best wishes
Dmitry