linux-kernel - Re: [PATCH 5/5] usb: dwc3: qcom: Allow runtime PM

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Message-ID: <ZCK3fGkgowvAd6Dw@hovoldconsulting.com>
Date:   Tue, 28 Mar 2023 11:46:36 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     andersson@...nel.org, Thinh.Nguyen@...opsys.com,
        gregkh@...uxfoundation.org, mathias.nyman@...el.com,
        konrad.dybcio@...aro.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 5/5] usb: dwc3: qcom: Allow runtime PM

On Sat, Mar 25, 2023 at 10:22:17PM +0530, Manivannan Sadhasivam wrote:
> dwc3-qcom driver is capable of doing runtime PM on its own, but currently
> it requires userspace intervention to enable it. But there is no harm in
> letting the driver to enable runtime PM on its own. So let's get rid of the
> "pm_runtime_forbid()" and make sure that the dependency is maintained with
> child devices using "pm_suspend_ignore_children(dev, false)".

Well, the potential harm is that these paths have hardly been tested so
enabling it by default is a risk (e.g. as you noticed when trying to
enable this by default). And especially if we don't address the layering
violations first.

> Also during remove(), the device needs to be waken up first if it was
> runtime suspended. Finally, pm_runtime_allow() can be removed.
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
>  drivers/usb/dwc3/dwc3-qcom.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
> index f1059dfcb0e8..5f26bb66274f 100644
> --- a/drivers/usb/dwc3/dwc3-qcom.c
> +++ b/drivers/usb/dwc3/dwc3-qcom.c
> @@ -920,7 +920,7 @@ static int dwc3_qcom_probe(struct platform_device *pdev)
>  	qcom->is_suspended = false;
>  	pm_runtime_set_active(dev);
>  	pm_runtime_enable(dev);
> -	pm_runtime_forbid(dev);
> +	pm_suspend_ignore_children(dev, false);

There's no need to explicitly disable ignore-children as that is the
default.

>  	return 0;
>  
> @@ -948,6 +948,8 @@ static int dwc3_qcom_remove(struct platform_device *pdev)
>  	struct device *dev = &pdev->dev;
>  	int i;
>  
> +	pm_runtime_get_sync(dev);

This call needs to be balanced. But this is a fix for a bug in the
current implementation that should go in a separate patch.

> +
>  	device_remove_software_node(&qcom->dwc3->dev);
>  	of_platform_depopulate(dev);
>  
> @@ -960,7 +962,6 @@ static int dwc3_qcom_remove(struct platform_device *pdev)
>  	dwc3_qcom_interconnect_exit(qcom);
>  	reset_control_assert(qcom->resets);
>  
> -	pm_runtime_allow(dev);
>  	pm_runtime_disable(dev);
>  
>  	return 0;

Johan