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

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Message-ID: <eb0d4f62-5dde-4a63-8515-23081ec9962c@quicinc.com>
Date: Mon, 19 Aug 2024 23:18:15 +0530
From: Krishna Kurapati <quic_kriskura@...cinc.com>
To: Bjorn Andersson <andersson@...nel.org>,
        Thinh Nguyen
	<Thinh.Nguyen@...opsys.com>
CC: <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>,
        Bjorn Andersson <quic_bjorande@...cinc.com>,
        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 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.

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