Re: [PATCH v4 3/9] usb: cdns3-ti: move reg writes from probe into ->runtime_resume()

From: "Théo Lebrun" <theo.lebrun@bootlin.com>
To: "Roger Quadros" <rogerq@kernel.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
	"Conor Dooley" <conor+dt@kernel.org>,
	"Peter Chen" <peter.chen@kernel.org>,
	"Pawel Laszczak" <pawell@cadence.com>,
	"Nishanth Menon" <nm@ti.com>,
	"Vignesh Raghavendra" <vigneshr@ti.com>,
	"Tero Kristo" <kristo@kernel.org>
Cc: "Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
	"Grégory Clement" <gregory.clement@bootlin.com>,
	"Kevin Hilman" <khilman@kernel.org>,
	"Alan Stern" <stern@rowland.harvard.edu>,
	linux-usb@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v4 3/9] usb: cdns3-ti: move reg writes from probe into ->runtime_resume()
Date: Thu, 07 Mar 2024 15:39:15 +0100	[thread overview]
Message-ID: <CZNLFUH8WWIA.MAUN8E53X7PK@bootlin.com> (raw)
In-Reply-To: <d1ca5d29-8ef4-4d7f-b1c8-bcb361e6c351@kernel.org>

Hello Roger,

On Thu Mar 7, 2024 at 1:31 PM CET, Roger Quadros wrote:
> Hi,
>
> On 07/03/2024 11:55, Théo Lebrun wrote:
> > The hardware initialisation register write sequence is only used at
> > probe. Move it from being done at explicitely at probe to being done
> > implicitely by pm_runtime_get_sync() that calls ->runtime_resume().
>
> explicitly / implicitly
>
> > 
> > Keep devicetree parsing in probe and add a new field in the private
> > struct to remember the USB2 refclk rate code computation result.
> > 
> > This opens the door to having the init sequence being executed later
> > down the road, at system-wide resume for example. This is NOT currently
> > happening because runtime PM is disabled at suspend without the
> > refcount being affected.
> > 
> > Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
> > ---
> >  drivers/usb/cdns3/cdns3-ti.c | 90 +++++++++++++++++++++++++-------------------
> >  1 file changed, 52 insertions(+), 38 deletions(-)
> > 
> > diff --git a/drivers/usb/cdns3/cdns3-ti.c b/drivers/usb/cdns3/cdns3-ti.c
> > index 5945c4b1e11f..4c8a557e6a6f 100644
> > --- a/drivers/usb/cdns3/cdns3-ti.c
> > +++ b/drivers/usb/cdns3/cdns3-ti.c
> > @@ -57,6 +57,7 @@ struct cdns_ti {
> >  	unsigned vbus_divider:1;
> >  	struct clk *usb2_refclk;
> >  	struct clk *lpm_clk;
> > +	int usb2_refclk_rate_code;
> >  };
> >  
> >  static const int cdns_ti_rate_table[] = {	/* in KHZ */
> > @@ -90,10 +91,8 @@ static int cdns_ti_probe(struct platform_device *pdev)
> >  	struct device *dev = &pdev->dev;
> >  	struct device_node *node = pdev->dev.of_node;
> >  	struct cdns_ti *data;
> > -	int error;
> > -	u32 reg;
> > -	int rate_code, i;
> >  	unsigned long rate;
> > +	int error, i;
> >  
> >  	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
> >  	if (!data)
> > @@ -133,7 +132,9 @@ static int cdns_ti_probe(struct platform_device *pdev)
> >  		return -EINVAL;
> >  	}
> >  
> > -	rate_code = i;
> > +	data->usb2_refclk_rate_code = i;
> > +	data->vbus_divider = device_property_read_bool(dev, "ti,vbus-divider");
> > +	data->usb2_only = device_property_read_bool(dev, "ti,usb2-only");
> >  
> >  	pm_runtime_enable(dev);
> >  	error = pm_runtime_get_sync(dev);
> > @@ -142,40 +143,6 @@ static int cdns_ti_probe(struct platform_device *pdev)
> >  		goto err;
> >  	}
> >  
> > -	/* assert RESET */
> > -	reg = cdns_ti_readl(data, USBSS_W1);
> > -	reg &= ~USBSS_W1_PWRUP_RST;
> > -	cdns_ti_writel(data, USBSS_W1, reg);
> > -
> > -	/* set static config */
> > -	reg = cdns_ti_readl(data, USBSS_STATIC_CONFIG);
> > -	reg &= ~USBSS1_STATIC_PLL_REF_SEL_MASK;
> > -	reg |= rate_code << USBSS1_STATIC_PLL_REF_SEL_SHIFT;
> > -
> > -	reg &= ~USBSS1_STATIC_VBUS_SEL_MASK;
> > -	data->vbus_divider = device_property_read_bool(dev, "ti,vbus-divider");
> > -	if (data->vbus_divider)
> > -		reg |= 1 << USBSS1_STATIC_VBUS_SEL_SHIFT;
> > -
> > -	cdns_ti_writel(data, USBSS_STATIC_CONFIG, reg);
> > -	reg = cdns_ti_readl(data, USBSS_STATIC_CONFIG);
> > -
> > -	/* set USB2_ONLY mode if requested */
> > -	reg = cdns_ti_readl(data, USBSS_W1);
> > -	data->usb2_only = device_property_read_bool(dev, "ti,usb2-only");
> > -	if (data->usb2_only)
> > -		reg |= USBSS_W1_USB2_ONLY;
> > -
> > -	/* set default modestrap */
> > -	reg |= USBSS_W1_MODESTRAP_SEL;
> > -	reg &= ~USBSS_W1_MODESTRAP_MASK;
> > -	reg |= USBSS_MODESTRAP_MODE_NONE << USBSS_W1_MODESTRAP_SHIFT;
> > -	cdns_ti_writel(data, USBSS_W1, reg);
> > -
> > -	/* de-assert RESET */
> > -	reg |= USBSS_W1_PWRUP_RST;
> > -	cdns_ti_writel(data, USBSS_W1, reg);
> > -
> >  	error = of_platform_populate(node, NULL, NULL, dev);
> >  	if (error) {
> >  		dev_err(dev, "failed to create children: %d\n", error);
> > @@ -211,6 +178,52 @@ static void cdns_ti_remove(struct platform_device *pdev)
> >  	platform_set_drvdata(pdev, NULL);
> >  }
> >  
> > +static int cdns_ti_runtime_resume(struct device *dev)
> > +{
> > +	struct cdns_ti *data = dev_get_drvdata(dev);
> > +	u32 reg;
> > +
> > +	/* assert RESET */
> > +	reg = cdns_ti_readl(data, USBSS_W1);
> > +	reg &= ~USBSS_W1_PWRUP_RST;
> > +	cdns_ti_writel(data, USBSS_W1, reg);
> > +
> > +	/* set static config */
> > +	reg = cdns_ti_readl(data, USBSS_STATIC_CONFIG);
> > +	reg &= ~USBSS1_STATIC_PLL_REF_SEL_MASK;
> > +	reg |= data->usb2_refclk_rate_code << USBSS1_STATIC_PLL_REF_SEL_SHIFT;
> > +
> > +	reg &= ~USBSS1_STATIC_VBUS_SEL_MASK;
> > +
> > +	if (data->vbus_divider)
> > +		reg |= 1 << USBSS1_STATIC_VBUS_SEL_SHIFT;
> > +
> > +	cdns_ti_writel(data, USBSS_STATIC_CONFIG, reg);
> > +	reg = cdns_ti_readl(data, USBSS_STATIC_CONFIG);
> > +
> > +	/* set USB2_ONLY mode if requested */
> > +	reg = cdns_ti_readl(data, USBSS_W1);
> > +
> > +	if (data->usb2_only)
> > +		reg |= USBSS_W1_USB2_ONLY;
> > +
> > +	/* set default modestrap */
> > +	reg |= USBSS_W1_MODESTRAP_SEL;
> > +	reg &= ~USBSS_W1_MODESTRAP_MASK;
> > +	reg |= USBSS_MODESTRAP_MODE_NONE << USBSS_W1_MODESTRAP_SHIFT;
> > +	cdns_ti_writel(data, USBSS_W1, reg);
> > +
> > +	/* de-assert RESET */
> > +	reg |= USBSS_W1_PWRUP_RST;
> > +	cdns_ti_writel(data, USBSS_W1, reg);
>
> I don't think USB controller requires a reset and re-init between
> runtime suspend/resume.
>
> What you need is reset/re-init during system Resume on certain platforms.
> So you should move this part of code into a helper function and call it
> from .probe() and .system_resume()

Runtime resume is being called at probe() and system-wide resume. See
our runtime_resume() implementation as that helper function you are
describing.

A previous revision did what you are recommending. We leaned towards the
current version. See:
https://lore.kernel.org/lkml/7h34wxfmwn.fsf@baylibre.com/

Also, assuming we enable runtime PM, a reset and re-init after runtime
suspend would be the right thing to do anyways. My reading of
drivers/pmdomain/core.c tells me that if our device goes to runtime
suspend, domains will be shut down. Our controller will be reset and
we'll need to re-init it. The GENPD_FLAG_RPM_ALWAYS_ON flag is of
interest to avoid the PD to be shut down during runtime PM.

Regards,

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