linux-kernel - Re: [PATCH v2 4/7] usb: dwc3: core: Expose core driver as library

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Message-ID: <ZsO62fLuftny3NfB@hu-bjorande-lv.qualcomm.com>
Date: Mon, 19 Aug 2024 14:36:25 -0700
From: Bjorn Andersson <quic_bjorande@...cinc.com>
To: Krishna Kurapati <quic_kriskura@...cinc.com>
CC: Bjorn Andersson <andersson@...nel.org>,
        Thinh Nguyen
	<Thinh.Nguyen@...opsys.com>, <linux-usb@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "Greg
 Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Rob Herring <robh@...nel.org>, Wesley Cheng <quic_wcheng@...cinc.com>,
        <linux-arm-msm@...r.kernel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Philipp Zabel
	<p.zabel@...gutronix.de>,
        Saravana Kannan <saravanak@...gle.com>,
        "Felipe
 Balbi" <balbi@...nel.org>
Subject: Re: [PATCH v2 4/7] usb: dwc3: core: Expose core driver as library

On Mon, Aug 19, 2024 at 11:18:15PM +0530, Krishna Kurapati wrote:
> 
> 
> On 8/12/2024 8:42 AM, Bjorn Andersson wrote:
> > From: Bjorn Andersson <quic_bjorande@...cinc.com>
> > 
> > The DWC3 IP block is handled by three distinct device drivers: XHCI,
> > DWC3 core and a platform specific (optional) DWC3 glue driver.
> > 
> > This has resulted in, at least in the case of the Qualcomm glue, the
> > presence of a number of layering violations, where the glue code either
> > can't handle, or has to work around, the fact that core might not probe
> > deterministically.
> > 
> > An example of this is that the suspend path should operate slightly
> > different depending on the device operating in host or peripheral mode,
> > and the only way to determine the operating state is to peek into the
> > core's drvdata.
> > 
> > The Qualcomm glue driver is expected to make updates in the qscratch
> > register region (the "glue" region) during role switch events, but with
> > the glue and core split using the driver model, there is no reasonable
> > way to introduce listeners for mode changes.
> > 
> > Split the dwc3 core platform_driver callbacks and their implementation
> > and export the implementation, to make it possible to deterministically
> > instantiate the dwc3 core as part of the dwc3 glue drivers and to
> > allow flattening of the DeviceTree representation.
> > 
> > Signed-off-by: Bjorn Andersson <quic_bjorande@...cinc.com>
> 
> ...
> 
> > -static int dwc3_probe(struct platform_device *pdev)
> > +struct dwc3 *dwc3_probe(struct platform_device *pdev, struct resource *res,
> > +			bool ignore_clocks_and_resets, void *glue)
> >   {
> >   	struct device		*dev = &pdev->dev;
> > -	struct resource		*res, dwc_res;
> > +	struct resource		dwc_res;
> >   	unsigned int		hw_mode;
> >   	void __iomem		*regs;
> >   	struct dwc3		*dwc;
> > @@ -2087,15 +2089,10 @@ static int dwc3_probe(struct platform_device *pdev)
> >   	dwc = devm_kzalloc(dev, sizeof(*dwc), GFP_KERNEL);
> >   	if (!dwc)
> > -		return -ENOMEM;
> > +		return ERR_PTR(-ENOMEM);
> >   	dwc->dev = dev;
> > -
> > -	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > -	if (!res) {
> > -		dev_err(dev, "missing memory resource\n");
> > -		return -ENODEV;
> > -	}
> 
> ...
> 
> > +static int dwc3_plat_probe(struct platform_device *pdev)
> >   {
> > -	struct dwc3	*dwc = platform_get_drvdata(pdev);
> > +	struct resource *res;
> > +	struct dwc3 *dwc;
> > +
> > +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > +	if (!res) {
> > +		dev_err(&pdev->dev, "missing memory resource\n");
> > +		return -ENODEV;
> > +	}
> > -	pm_runtime_get_sync(&pdev->dev);
> > +	dwc = dwc3_probe(pdev, res, false, NULL);
> > +	if (IS_ERR(dwc))
> > +		return PTR_ERR(dwc);
> > +
> > +	platform_set_drvdata(pdev, dwc);
> 
> This setting of platform drvdata is redundant I believe. We already do it in
> dwc3_probe.
> 

Good catch, you're certainly right.

Regards,
Bjorn

> > +
> > +	return 0;
> > +}
> > +