linux-kernel - Re: [PATCH 3/6] usb: cdns3-ti: add suspend/resume procedures for J7200

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Date:   Wed, 15 Nov 2023 16:02:37 +0100
From:   Théo Lebrun <theo.lebrun@...tlin.com>
To:     "Roger Quadros" <rogerq@...nel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        "Conor Dooley" <conor+dt@...nel.org>,
        "Peter Chen" <peter.chen@...nel.org>,
        "Pawel Laszczak" <pawell@...ence.com>,
        "Nishanth Menon" <nm@...com>,
        "Vignesh Raghavendra" <vigneshr@...com>,
        "Tero Kristo" <kristo@...nel.org>
Cc:     <linux-usb@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/6] usb: cdns3-ti: add suspend/resume procedures for
 J7200

Hi Roger,

On Wed Nov 15, 2023 at 12:37 PM CET, Roger Quadros wrote:
> On 13/11/2023 16:26, Théo Lebrun wrote:
> > Hardware initialisation is only done at probe. The J7200 USB controller
> > is reset at resume because of power-domains toggling off & on. We
> > therefore (1) toggle PM runtime at suspend/resume & (2) reconfigure the
> > hardware at resume.
>
> at probe we are doing a pm_runtime_get() and never doing a put thus
> preventing any runtime PM.

Indeed. The get() from probe/resume are in symmetry with the put() from
suspend. Is this wrong in some manner?

> > index c331bcd2faeb..50b38c4b9c87 100644
> > --- a/drivers/usb/cdns3/cdns3-ti.c
> > +++ b/drivers/usb/cdns3/cdns3-ti.c
> > @@ -197,6 +197,50 @@ static int cdns_ti_probe(struct platform_device *pdev)
> >  	return error;
> >  }
> >  
> > +#ifdef CONFIG_PM
> > +
> > +static int cdns_ti_suspend(struct device *dev)
> > +{
> > +	struct cdns_ti *data = dev_get_drvdata(dev);
> > +
> > +	if (!of_device_is_compatible(dev_of_node(dev), "ti,j7200-usb"))
> > +		return 0;
> > +
> > +	pm_runtime_put_sync(data->dev);
> > +
> > +	return 0;
>
> You might want to check suspend/resume ops in cdns3-plat and
> do something similar here.

I'm unsure what you are referring to specifically in cdns3-plat?

 - Using pm_runtime_status_suspended() to get the current PM runtime
   state & act on it? I don't see why because we know the pm_runtime
   state is a single put() at probe.

 - Having a `in_lpm` flag to track low-power mode state? I wouldn't see
   why we'd want that as we don't register runtime_suspend &
   runtime_resume callbacks and system syspend/resume can be assumed to
   be called in the right order.

 - Checking the `device_may_wakeup()`? That doesn't apply to this driver
   which cannot be a wakeup source.

Thanks for your review!
Regards,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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