Message-ID: <20250813192957.GA286749@bhelgaas>
Date: Wed, 13 Aug 2025 14:29:57 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Christian Bruel <christian.bruel@...s.st.com>
Cc: lpieralisi@...nel.org, kwilczynski@...nel.org, mani@...nel.org,
	robh@...nel.org, bhelgaas@...gle.com, krzk+dt@...nel.org,
	conor+dt@...nel.org, mcoquelin.stm32@...il.com,
	alexandre.torgue@...s.st.com, p.zabel@...gutronix.de,
	johan+linaro@...nel.org, cassel@...nel.org, shradha.t@...sung.com,
	thippeswamy.havalige@....com, quic_schintav@...cinc.com,
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 2/9] PCI: stm32: Add PCIe host support for STM32MP25

On Tue, Jun 10, 2025 at 11:07:07AM +0200, Christian Bruel wrote:
> Add driver for the STM32MP25 SoC PCIe Gen1 2.5 GT/s and Gen2 5GT/s
> controller based on the DesignWare PCIe core.
> ...

> +struct stm32_pcie {
> +	struct dw_pcie pci;
> +	struct regmap *regmap;
> +	struct reset_control *rst;
> +	struct phy *phy;
> +	struct clk *clk;
> +	struct gpio_desc *perst_gpio;
> +	struct gpio_desc *wake_gpio;
> +};
> +
> +static void stm32_pcie_deassert_perst(struct stm32_pcie *stm32_pcie)
> +{
> +	/* Delay PERST# de-assertion until the power stabilizes */
> +	msleep(PCIE_T_PVPERL_MS);
> +
> +	gpiod_set_value(stm32_pcie->perst_gpio, 0);
> +
> +	/* Wait for the REFCLK to stabilize */
> +	if (stm32_pcie->perst_gpio)
> +		msleep(PCIE_T_RRS_READY_MS);

This obviously relies on gpiod_set_value(stm32_pcie->perst_gpio, 0)
being a no-op when perst_gpio == NULL.  Since we're testing perst_gpio
anyway, I think it might be more readable to avoid relying on
gpiod_set_value() being a no-op:

  msleep(PCIE_T_PVPERL_MS);

  if (stm32_pcie->perst_gpio) {
    gpiod_set_value(stm32_pcie->perst_gpio, 0);
    msleep(PCIE_T_RRS_READY_MS);
  }

(And a similar change in stm32_pcie_assert_perst())

But this seems wrong because PCIE_T_PVPERL_MS is a delay before PERST#
is deasserted, but when perst_gpio == NULL, PERST# has already *been*
deasserted.

So it seems like it would make more sense as:

  if (stm32_pcie->perst_gpio) {
    msleep(PCIE_T_PVPERL_MS);
    gpiod_set_value(stm32_pcie->perst_gpio, 0);
  }

  msleep(PCIE_T_RRS_READY_MS);

> +}
> +
> +static void stm32_pcie_assert_perst(struct stm32_pcie *stm32_pcie)
> +{
> +	gpiod_set_value(stm32_pcie->perst_gpio, 1);
> +}
> +
> +static int stm32_pcie_start_link(struct dw_pcie *pci)
> +{
> +	struct stm32_pcie *stm32_pcie = to_stm32_pcie(pci);
> +
> +	return regmap_update_bits(stm32_pcie->regmap, SYSCFG_PCIECR,
> +				  STM32MP25_PCIECR_LTSSM_EN,
> +				  STM32MP25_PCIECR_LTSSM_EN);
> +}
> +
> +static void stm32_pcie_stop_link(struct dw_pcie *pci)
> +{
> +	struct stm32_pcie *stm32_pcie = to_stm32_pcie(pci);
> +
> +	regmap_update_bits(stm32_pcie->regmap, SYSCFG_PCIECR,
> +			   STM32MP25_PCIECR_LTSSM_EN, 0);
> +}
> +
> +static int stm32_pcie_suspend_noirq(struct device *dev)
> +{
> +	struct stm32_pcie *stm32_pcie = dev_get_drvdata(dev);
> +	int ret;
> +
> +	ret = dw_pcie_suspend_noirq(&stm32_pcie->pci);
> +	if (ret)
> +		return ret;
> +
> +	stm32_pcie_assert_perst(stm32_pcie);
> +
> +	clk_disable_unprepare(stm32_pcie->clk);
> +
> +	if (!device_wakeup_path(dev))
> +		phy_exit(stm32_pcie->phy);
> +
> +	return pinctrl_pm_select_sleep_state(dev);
> +}
> +
> +static int stm32_pcie_resume_noirq(struct device *dev)
> +{
> +	struct stm32_pcie *stm32_pcie = dev_get_drvdata(dev);
> +	int ret;
> +
> +	/*
> +	 * The core clock is gated with CLKREQ# from the COMBOPHY REFCLK,
> +	 * thus if no device is present, must force it low with an init pinmux
> +	 * to be able to access the DBI registers.

What happens on initial probe if no device is present?  I assume we
access DBI registers in the dw_pcie_host_init() path, and it seems
like we'd have the same issue with DBI not being accessible when no
device is present.

> +	if (!IS_ERR(dev->pins->init_state))
> +		ret = pinctrl_select_state(dev->pins->p, dev->pins->init_state);
> +	else
> +		ret = pinctrl_pm_select_default_state(dev);
> +
> +	if (ret) {
> +		dev_err(dev, "Failed to activate pinctrl pm state: %d\n", ret);
> +		return ret;
> +	}
> +
> +	if (!device_wakeup_path(dev)) {
> +		ret = phy_init(stm32_pcie->phy);
> +		if (ret) {
> +			pinctrl_pm_select_default_state(dev);
> +			return ret;
> +		}
> +	}
> +
> +	ret = clk_prepare_enable(stm32_pcie->clk);
> +	if (ret)
> +		goto err_phy_exit;
> +
> +	stm32_pcie_deassert_perst(stm32_pcie);
> +
> +	ret = dw_pcie_resume_noirq(&stm32_pcie->pci);
> +	if (ret)
> +		goto err_disable_clk;
> +
> +	pinctrl_pm_select_default_state(dev);
> +
> +	return 0;
> +
> +err_disable_clk:
> +	stm32_pcie_assert_perst(stm32_pcie);
> +	clk_disable_unprepare(stm32_pcie->clk);
> +
> +err_phy_exit:
> +	phy_exit(stm32_pcie->phy);
> +	pinctrl_pm_select_default_state(dev);
> +
> +	return ret;
> +}
> +
> +static const struct dev_pm_ops stm32_pcie_pm_ops = {
> +	NOIRQ_SYSTEM_SLEEP_PM_OPS(stm32_pcie_suspend_noirq,
> +				  stm32_pcie_resume_noirq)
> +};
> +
> +static const struct dw_pcie_host_ops stm32_pcie_host_ops = {
> +};
> +
> +static const struct dw_pcie_ops dw_pcie_ops = {
> +	.start_link = stm32_pcie_start_link,
> +	.stop_link = stm32_pcie_stop_link
> +};
> +
> +static int stm32_add_pcie_port(struct stm32_pcie *stm32_pcie)
> +{
> +	struct device *dev = stm32_pcie->pci.dev;
> +	unsigned int wake_irq;
> +	int ret;
> +
> +	/* Start to enable resources with PERST# asserted */

I guess if device tree doesn't describe PERST#, we assume PERST# is
actually *deasserted* already at this point (because
stm32_pcie_deassert_perst() does nothing other than the delay)?

> +	ret = phy_set_mode(stm32_pcie->phy, PHY_MODE_PCIE);
> +	if (ret)
> +		return ret;
> +
> +	ret = phy_init(stm32_pcie->phy);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_update_bits(stm32_pcie->regmap, SYSCFG_PCIECR,
> +				 STM32MP25_PCIECR_TYPE_MASK,
> +				 STM32MP25_PCIECR_RC);
> +	if (ret)
> +		goto err_phy_exit;
> +
> +	stm32_pcie_deassert_perst(stm32_pcie);
> +
> +	if (stm32_pcie->wake_gpio) {
> +		wake_irq = gpiod_to_irq(stm32_pcie->wake_gpio);
> +		ret = dev_pm_set_dedicated_wake_irq(dev, wake_irq);
> +		if (ret) {
> +			dev_err(dev, "Failed to enable wakeup irq %d\n", ret);
> +			goto err_assert_perst;
> +		}
> +		irq_set_irq_type(wake_irq, IRQ_TYPE_EDGE_FALLING);
> +	}
> +
> +	return 0;
> +
> +err_assert_perst:
> +	stm32_pcie_assert_perst(stm32_pcie);
> +
> +err_phy_exit:
> +	phy_exit(stm32_pcie->phy);
> +
> +	return ret;
> +}
> +
> +static void stm32_remove_pcie_port(struct stm32_pcie *stm32_pcie)
> +{
> +	dev_pm_clear_wake_irq(stm32_pcie->pci.dev);
> +
> +	stm32_pcie_assert_perst(stm32_pcie);
> +
> +	phy_exit(stm32_pcie->phy);
> +}
> +
> +static int stm32_pcie_parse_port(struct stm32_pcie *stm32_pcie)
> +{
> +	struct device *dev = stm32_pcie->pci.dev;
> +	struct device_node *root_port;
> +
> +	root_port = of_get_next_available_child(dev->of_node, NULL);
> +
> +	stm32_pcie->phy = devm_of_phy_get(dev, root_port, NULL);
> +	if (IS_ERR(stm32_pcie->phy)) {
> +		of_node_put(root_port);
> +		return dev_err_probe(dev, PTR_ERR(stm32_pcie->phy),
> +				     "Failed to get pcie-phy\n");
> +	}
> +
> +	stm32_pcie->perst_gpio = devm_fwnode_gpiod_get(dev, of_fwnode_handle(root_port),
> +						       "reset", GPIOD_OUT_HIGH, NULL);
> +	if (IS_ERR(stm32_pcie->perst_gpio)) {
> +		if (PTR_ERR(stm32_pcie->perst_gpio) != -ENOENT) {
> +			of_node_put(root_port);
> +			return dev_err_probe(dev, PTR_ERR(stm32_pcie->perst_gpio),
> +					     "Failed to get reset GPIO\n");
> +		}
> +		stm32_pcie->perst_gpio = NULL;

This looks like perst_gpio is optional in device tree?  Is that really
the case?  It seems hard to ensure we have the PCIE_T_PVPERL_MS and
PCIE_T_RRS_READY_MS delays in the right place if we don't have
perst_gpio.

> +	}
> +
> +	stm32_pcie->wake_gpio = devm_fwnode_gpiod_get(dev, of_fwnode_handle(root_port),
> +						      "wake", GPIOD_IN, NULL);
> +
> +	if (IS_ERR(stm32_pcie->wake_gpio)) {
> +		if (PTR_ERR(stm32_pcie->wake_gpio) != -ENOENT) {
> +			of_node_put(root_port);
> +			return dev_err_probe(dev, PTR_ERR(stm32_pcie->wake_gpio),
> +					     "Failed to get wake GPIO\n");
> +		}
> +		stm32_pcie->wake_gpio = NULL;
> +	}
> +
> +	of_node_put(root_port);
> +
> +	return 0;
> +}
> +
> +static int stm32_pcie_probe(struct platform_device *pdev)
> +{
> +	struct stm32_pcie *stm32_pcie;
> +	struct device *dev = &pdev->dev;
> +	int ret;
> +
> +	stm32_pcie = devm_kzalloc(dev, sizeof(*stm32_pcie), GFP_KERNEL);
> +	if (!stm32_pcie)
> +		return -ENOMEM;
> +
> +	stm32_pcie->pci.dev = dev;
> +	stm32_pcie->pci.ops = &dw_pcie_ops;
> +	stm32_pcie->pci.pp.ops = &stm32_pcie_host_ops;
> +
> +	stm32_pcie->regmap = syscon_regmap_lookup_by_compatible("st,stm32mp25-syscfg");
> +	if (IS_ERR(stm32_pcie->regmap))
> +		return dev_err_probe(dev, PTR_ERR(stm32_pcie->regmap),
> +				     "No syscfg specified\n");
> +
> +	stm32_pcie->clk = devm_clk_get(dev, NULL);
> +	if (IS_ERR(stm32_pcie->clk))
> +		return dev_err_probe(dev, PTR_ERR(stm32_pcie->clk),
> +				     "Failed to get PCIe clock source\n");
> +
> +	stm32_pcie->rst = devm_reset_control_get_exclusive(dev, NULL);
> +	if (IS_ERR(stm32_pcie->rst))
> +		return dev_err_probe(dev, PTR_ERR(stm32_pcie->rst),
> +				     "Failed to get PCIe reset\n");
> +
> +	ret = stm32_pcie_parse_port(stm32_pcie);
> +	if (ret)
> +		return ret;
> +
> +	platform_set_drvdata(pdev, stm32_pcie);
> +
> +	ret = stm32_add_pcie_port(stm32_pcie);
> +	if (ret)
> +		return ret;
> +
> +	reset_control_assert(stm32_pcie->rst);
> +	reset_control_deassert(stm32_pcie->rst);
> +
> +	ret = clk_prepare_enable(stm32_pcie->clk);
> +	if (ret) {
> +		dev_err(dev, "Core clock enable failed %d\n", ret);
> +		goto err_remove_port;
> +	}
> +
> +	ret = pm_runtime_set_active(dev);
> +	if (ret < 0) {
> +		clk_disable_unprepare(stm32_pcie->clk);
> +		stm32_remove_pcie_port(stm32_pcie);
> +		return dev_err_probe(dev, ret, "Failed to activate runtime PM\n");
> +	}
> +
> +	pm_runtime_no_callbacks(dev);
> +
> +	ret = devm_pm_runtime_enable(dev);
> +	if (ret < 0) {
> +		clk_disable_unprepare(stm32_pcie->clk);
> +		stm32_remove_pcie_port(stm32_pcie);
> +		return dev_err_probe(dev, ret, "Failed to enable runtime PM\n");
> +	}
> +
> +	ret = dw_pcie_host_init(&stm32_pcie->pci.pp);
> +	if (ret)
> +		goto err_disable_clk;
> +
> +	if (stm32_pcie->wake_gpio)
> +		device_init_wakeup(dev, true);
> +
> +	return 0;
> +
> +err_disable_clk:
> +	clk_disable_unprepare(stm32_pcie->clk);
> +
> +err_remove_port:
> +	stm32_remove_pcie_port(stm32_pcie);
> +
> +	return ret;
> +}
> +
> +static void stm32_pcie_remove(struct platform_device *pdev)
> +{
> +	struct stm32_pcie *stm32_pcie = platform_get_drvdata(pdev);
> +	struct dw_pcie_rp *pp = &stm32_pcie->pci.pp;
> +
> +	if (stm32_pcie->wake_gpio)
> +		device_init_wakeup(&pdev->dev, false);
> +
> +	dw_pcie_host_deinit(pp);
> +
> +	clk_disable_unprepare(stm32_pcie->clk);
> +
> +	stm32_remove_pcie_port(stm32_pcie);
> +
> +	pm_runtime_put_noidle(&pdev->dev);
> +}
> +
> +static const struct of_device_id stm32_pcie_of_match[] = {
> +	{ .compatible = "st,stm32mp25-pcie-rc" },
> +	{},
> +};
> +
> +static struct platform_driver stm32_pcie_driver = {
> +	.probe = stm32_pcie_probe,
> +	.remove = stm32_pcie_remove,
> +	.driver = {
> +		.name = "stm32-pcie",
> +		.of_match_table = stm32_pcie_of_match,
> +		.pm = &stm32_pcie_pm_ops,
> +		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
> +	},
> +};
> +
> +module_platform_driver(stm32_pcie_driver);
> +
> +MODULE_AUTHOR("Christian Bruel <christian.bruel@...s.st.com>");
> +MODULE_DESCRIPTION("STM32MP25 PCIe Controller driver");
> +MODULE_LICENSE("GPL");
> +MODULE_DEVICE_TABLE(of, stm32_pcie_of_match);
> diff --git a/drivers/pci/controller/dwc/pcie-stm32.h b/drivers/pci/controller/dwc/pcie-stm32.h
> new file mode 100644
> index 000000000000..387112c4e42c
> --- /dev/null
> +++ b/drivers/pci/controller/dwc/pcie-stm32.h
> @@ -0,0 +1,15 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * ST PCIe driver definitions for STM32-MP25 SoC
> + *
> + * Copyright (C) 2025 STMicroelectronics - All Rights Reserved
> + * Author: Christian Bruel <christian.bruel@...s.st.com>
> + */
> +
> +#define to_stm32_pcie(x)	dev_get_drvdata((x)->dev)
> +
> +#define STM32MP25_PCIECR_TYPE_MASK	GENMASK(11, 8)
> +#define STM32MP25_PCIECR_LTSSM_EN	BIT(2)
> +#define STM32MP25_PCIECR_RC		BIT(10)
> +
> +#define SYSCFG_PCIECR			0x6000
> -- 
> 2.34.1
> 

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