Message-ID: <d2e9a521-568e-433d-a59b-9b98138ace2b@ieee.org>
Date: Tue, 15 Jul 2025 15:50:54 -0500
From: Alex Elder <elder@...e.org>
To: Ze Huang <huang.ze@...ux.dev>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Yixun Lan <dlan@...too.org>,
 Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
 Philipp Zabel <p.zabel@...gutronix.de>
Cc: linux-usb@...r.kernel.org, devicetree@...r.kernel.org,
 linux-riscv@...ts.infradead.org, spacemit@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/2] usb: dwc3: add generic driver to support flattened

On 7/12/25 2:49 AM, Ze Huang wrote:
> To support flattened dwc3 dt model and drop the glue layer, introduce the
> `dwc3-generic` driver. This enables direct binding of the DWC3 core driver
> and offers an alternative to the existing glue driver `dwc3-of-simple`.

I'm not familiar with dwc-of-simple.c, and won't comment on
how this differs from that (or does not).

Given you're implementing an alternative though, can you explain
in a little more detail what's different between the two?  Why
would someone choose to use this driver rather than the other one?

> 
> Signed-off-by: Ze Huang <huang.ze@...ux.dev>
> ---
>   drivers/usb/dwc3/Kconfig             |  11 +++
>   drivers/usb/dwc3/Makefile            |   1 +
>   drivers/usb/dwc3/dwc3-generic-plat.c | 182 +++++++++++++++++++++++++++++++++++
>   3 files changed, 194 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/Kconfig b/drivers/usb/dwc3/Kconfig
> index 310d182e10b50b253d7e5a51674806e6ec442a2a..4925d15084f816d3ff92059b476ebcc799b56b51 100644
> --- a/drivers/usb/dwc3/Kconfig
> +++ b/drivers/usb/dwc3/Kconfig
> @@ -189,4 +189,15 @@ config USB_DWC3_RTK
>   	  or dual-role mode.
>   	  Say 'Y' or 'M' if you have such device.
>   
> +config USB_DWC3_GENERIC_PLAT
> +	tristate "DWC3 Generic Platform Driver"
> +	depends on OF && COMMON_CLK
> +	default USB_DWC3
> +	help
> +	  Support USB3 functionality in simple SoC integrations.
> +	  Currently supports SpacemiT DWC USB3. Platforms using
> +	  dwc3-of-simple can easily switch to dwc3-generic by flattening
> +	  the dwc3 child node in the device tree.
> +	  Say 'Y' or 'M' here if your platform integrates DWC3 in a similar way.
> +
>   endif
> diff --git a/drivers/usb/dwc3/Makefile b/drivers/usb/dwc3/Makefile
> index 830e6c9e5fe073c1f662ce34b6a4a2da34c407a2..96469e48ff9d189cc8d0b65e65424eae2158bcfe 100644
> --- a/drivers/usb/dwc3/Makefile
> +++ b/drivers/usb/dwc3/Makefile
> @@ -57,3 +57,4 @@ obj-$(CONFIG_USB_DWC3_IMX8MP)		+= dwc3-imx8mp.o
>   obj-$(CONFIG_USB_DWC3_XILINX)		+= dwc3-xilinx.o
>   obj-$(CONFIG_USB_DWC3_OCTEON)		+= dwc3-octeon.o
>   obj-$(CONFIG_USB_DWC3_RTK)		+= dwc3-rtk.o
> +obj-$(CONFIG_USB_DWC3_GENERIC_PLAT)	+= dwc3-generic-plat.o
> diff --git a/drivers/usb/dwc3/dwc3-generic-plat.c b/drivers/usb/dwc3/dwc3-generic-plat.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..766f4cf17b6909793956f44660d3b3febad50a23
> --- /dev/null
> +++ b/drivers/usb/dwc3/dwc3-generic-plat.c
> @@ -0,0 +1,182 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * dwc3-generic-plat.c - DesignWare USB3 generic platform driver
> + *
> + * Copyright (C) 2025 Ze Huang <huang.ze@...ux.dev>
> + *
> + * Inspired by dwc3-qcom.c and dwc3-of-simple.c
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/platform_device.h>
> +#include <linux/reset.h>
> +#include "glue.h"
> +
> +struct dwc3_generic {
> +	struct device		*dev;
> +	struct dwc3		dwc;
> +	struct clk_bulk_data	*clks;
> +	int			num_clocks;
> +	struct reset_control	*resets;
> +};
> +
> +static void dwc3_generic_reset_control_assert(void *data)
> +{
> +	reset_control_assert(data);
> +}
> +

The next function can go away.  (See below.)

> +static void dwc3_generic_clk_bulk_disable_unprepare(void *data)
> +{
> +	struct dwc3_generic *dwc3 = data;
> +
> +	clk_bulk_disable_unprepare(dwc3->num_clocks, dwc3->clks);
> +}
> +
> +static int dwc3_generic_probe(struct platform_device *pdev)
> +{
> +	struct dwc3_probe_data probe_data = {};
> +	struct device *dev = &pdev->dev;
> +	struct dwc3_generic *dwc3;
> +	struct resource *res;
> +	int ret;
> +
> +	dwc3 = devm_kzalloc(dev, sizeof(*dwc3), GFP_KERNEL);
> +	if (!dwc3)
> +		return -ENOMEM;
> +
> +	dwc3->dev = dev;
> +
> +	platform_set_drvdata(pdev, dwc3);
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	if (!res) {
> +		dev_err(&pdev->dev, "missing memory resource\n");
> +		return -ENODEV;
> +	}
> +
> +	dwc3->resets = devm_reset_control_array_get_optional_exclusive(dev);
> +	if (IS_ERR(dwc3->resets))
> +		return dev_err_probe(dev, PTR_ERR(dwc3->resets), "failed to get resets\n");
> +

It isn't enforced on exclusive resets, but I'm pretty sure
resets are assumed to be asserted initially.

> +	ret = reset_control_assert(dwc3->resets);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "failed to assert resets\n");
> +
> +	ret = devm_add_action_or_reset(dev, dwc3_generic_reset_control_assert, dwc3->resets);
> +	if (ret)
> +		return ret;

The re-assert shouldn't be set up unless the deassert below
succeeds.

> +	usleep_range(10, 1000);

This seems like a large range.  You could just do msleep(1);
Also, can you add a comment explaining why a delay is needed,
and why 1 millisecond is the right amount of time to sleep?

> +	ret = reset_control_deassert(dwc3->resets);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "failed to deassert resets\n");
> +
> +	ret = devm_clk_bulk_get_all(dwc3->dev, &dwc3->clks);
> +	if (ret < 0)
> +		return dev_err_probe(dev, ret, "failed to get clocks\n");

Call devm_clk_bulk_get_all_enabled() instead of doing the two
steps separately here.

					-Alex

> +	dwc3->num_clocks = ret;
> +
> +	ret = clk_bulk_prepare_enable(dwc3->num_clocks, dwc3->clks);
> +	if (ret)
j> +		return dev_err_probe(dev, ret, "failed to enable clocks\n");
> +
> +	ret = devm_add_action_or_reset(dev, dwc3_generic_clk_bulk_disable_unprepare, dwc3);
> +	if (ret)
> +		return ret;
> +
> +	dwc3->dwc.dev = dev;
> +	probe_data.dwc = &dwc3->dwc;
> +	probe_data.res = res;
> +	probe_data.ignore_clocks_and_resets = true;
> +	ret = dwc3_core_probe(&probe_data);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "failed to register DWC3 Core\n");
> +
> +	return 0;
> +}
> +
> +static void dwc3_generic_remove(struct platform_device *pdev)
> +{
> +	struct dwc3_generic *dwc3 = platform_get_drvdata(pdev);
> +
> +	dwc3_core_remove(&dwc3->dwc);
> +}
> +
> +static int dwc3_generic_suspend(struct device *dev)
> +{
> +	struct dwc3_generic *dwc3 = dev_get_drvdata(dev);
> +	int ret;
> +
> +	ret = dwc3_pm_suspend(&dwc3->dwc);
> +	if (ret)
> +		return ret;
> +
> +	clk_bulk_disable_unprepare(dwc3->num_clocks, dwc3->clks);
> +
> +	return 0;
> +}
> +
> +static int dwc3_generic_resume(struct device *dev)
> +{
> +	struct dwc3_generic *dwc3 = dev_get_drvdata(dev);
> +	int ret;
> +
> +	ret = clk_bulk_prepare_enable(dwc3->num_clocks, dwc3->clks);
> +	if (ret)
> +		return ret;
> +
> +	ret = dwc3_pm_resume(&dwc3->dwc);
> +	if (ret)
> +		return ret;
> +
> +	return 0;
> +}
> +
> +static int dwc3_generic_runtime_suspend(struct device *dev)
> +{
> +	struct dwc3_generic *dwc3 = dev_get_drvdata(dev);
> +
> +	return dwc3_runtime_suspend(&dwc3->dwc);
> +}
> +
> +static int dwc3_generic_runtime_resume(struct device *dev)
> +{
> +	struct dwc3_generic *dwc3 = dev_get_drvdata(dev);
> +
> +	return dwc3_runtime_resume(&dwc3->dwc);
> +}
> +
> +static int dwc3_generic_runtime_idle(struct device *dev)
> +{
> +	struct dwc3_generic *dwc3 = dev_get_drvdata(dev);
> +
> +	return dwc3_runtime_idle(&dwc3->dwc);
> +}
> +
> +static const struct dev_pm_ops dwc3_generic_dev_pm_ops = {
> +	SYSTEM_SLEEP_PM_OPS(dwc3_generic_suspend, dwc3_generic_resume)
> +	RUNTIME_PM_OPS(dwc3_generic_runtime_suspend, dwc3_generic_runtime_resume,
> +		       dwc3_generic_runtime_idle)
> +};
> +
> +static const struct of_device_id dwc3_generic_of_match[] = {
> +	{ .compatible = "spacemit,k1-dwc3", },
> +	{ /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, dwc3_generic_of_match);
> +
> +static struct platform_driver dwc3_generic_driver = {
> +	.probe		= dwc3_generic_probe,
> +	.remove		= dwc3_generic_remove,
> +	.driver		= {
> +		.name	= "dwc3-generic-plat",
> +		.of_match_table = dwc3_generic_of_match,
> +		.pm	= pm_ptr(&dwc3_generic_dev_pm_ops),
> +	},
> +};
> +module_platform_driver(dwc3_generic_driver);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("DesignWare USB3 generic platform driver");
> 

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