linux-kernel - Re: [PATCH] PCI: qcom: Add support for modular builds

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Message-ID: <20220623155213.GA1450949@bhelgaas>
Date:   Thu, 23 Jun 2022 10:52:13 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Johan Hovold <johan+linaro@...nel.org>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Stanimir Varbanov <svarbanov@...sol.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: qcom: Add support for modular builds

On Thu, May 19, 2022 at 11:46:46AM +0200, Johan Hovold wrote:
> Allow the Qualcomm PCIe controller driver to be built as a module, which
> is useful for multi-platform kernels as well as during development.
> 
> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> ---
>  drivers/pci/controller/dwc/Kconfig     |  2 +-
>  drivers/pci/controller/dwc/pcie-qcom.c | 36 +++++++++++++++++++++++---
>  2 files changed, 34 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/Kconfig b/drivers/pci/controller/dwc/Kconfig
> index 62ce3abf0f19..230f56d1a268 100644
> --- a/drivers/pci/controller/dwc/Kconfig
> +++ b/drivers/pci/controller/dwc/Kconfig
> @@ -168,7 +168,7 @@ config PCI_HISI
>  	  Hip05 and Hip06 SoCs
>  
>  config PCIE_QCOM
> -	bool "Qualcomm PCIe controller"
> +	tristate "Qualcomm PCIe controller"
>  	depends on OF && (ARCH_QCOM || COMPILE_TEST)
>  	depends on PCI_MSI_IRQ_DOMAIN
>  	select PCIE_DW_HOST
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 8523b5ef9d16..e25d5c09657c 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -16,7 +16,7 @@
>  #include <linux/io.h>
>  #include <linux/iopoll.h>
>  #include <linux/kernel.h>
> -#include <linux/init.h>
> +#include <linux/module.h>
>  #include <linux/of_device.h>
>  #include <linux/of_gpio.h>
>  #include <linux/pci.h>
> @@ -1425,6 +1425,15 @@ static int qcom_pcie_host_init(struct pcie_port *pp)
>  	return ret;
>  }
>  
> +static void qcom_pcie_host_deinit(struct qcom_pcie *pcie)
> +{
> +	qcom_ep_reset_assert(pcie);
> +	if (pcie->cfg->ops->post_deinit)
> +		pcie->cfg->ops->post_deinit(pcie);
> +	phy_power_off(pcie->phy);
> +	pcie->cfg->ops->deinit(pcie);

These post_deinit/deinit names look backwards.  Why would we call a
"post_deinit()" method *before* the "deinit()" method?  It would make
sense if we called "pre_deinit()" followed by "deinit()".

>  static const struct dw_pcie_host_ops qcom_pcie_dw_ops = {
>  	.host_init = qcom_pcie_host_init,
>  };
> @@ -1651,6 +1660,22 @@ static int qcom_pcie_probe(struct platform_device *pdev)
>  	return ret;
>  }
>  
> +static int qcom_pcie_remove(struct platform_device *pdev)
> +{
> +	struct qcom_pcie *pcie = platform_get_drvdata(pdev);
> +	struct device *dev = &pdev->dev;
> +
> +	dw_pcie_host_deinit(&pcie->pci->pp);
> +	qcom_pcie_host_deinit(pcie);
> +
> +	phy_exit(pcie->phy);
> +
> +	pm_runtime_put_sync(dev);
> +	pm_runtime_disable(dev);

Why is this not more symmetric with qcom_pcie_probe()?  Maybe struct
dw_pcie_host_ops needs a new .host_deinit() pointer that would be
called from dw_pcie_host_deinit()?

In the probe path, we have this:

  qcom_pcie_probe
    pm_runtime_enable
    pm_runtime_get_sync
    phy_init(pcie->phy)
    dw_pcie_host_init
      pp->ops->host_init
        qcom_pcie_host_init             # .host_init()
          pcie->cfg->ops->init(pcie)
          phy_power_on(pcie->phy)
          pcie->cfg->ops->post_init(pcie)
          qcom_ep_reset_deassert(pcie)

The remove path does do things in the opposite order, which makes
sense, but the call to qcom_pcie_host_deinit() breaks the symmetry:

  qcom_pcie_remove
    dw_pcie_host_deinit
    qcom_pcie_host_deinit
      qcom_ep_reset_assert
      pcie->cfg->ops->post_deinit
      phy_power_off(pcie->phy)
      pcie->cfg->ops->deinit
    phy_exit(pcie->phy)
    pm_runtime_put_sync
    pm_runtime_disable

> +	return 0;
> +}
> +
>  static const struct of_device_id qcom_pcie_match[] = {
>  	{ .compatible = "qcom,pcie-apq8084", .data = &apq8084_cfg },
>  	{ .compatible = "qcom,pcie-ipq8064", .data = &ipq8064_cfg },
> @@ -1669,6 +1694,7 @@ static const struct of_device_id qcom_pcie_match[] = {
>  	{ .compatible = "qcom,pcie-sc7280", .data = &sc7280_cfg },
>  	{ }
>  };
> +MODULE_DEVICE_TABLE(of, qcom_pcie_match);
>  
>  static void qcom_fixup_class(struct pci_dev *dev)
>  {
> @@ -1684,10 +1710,14 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_QCOM, 0x1001, qcom_fixup_class);
>  
>  static struct platform_driver qcom_pcie_driver = {
>  	.probe = qcom_pcie_probe,
> +	.remove = qcom_pcie_remove,
>  	.driver = {
>  		.name = "qcom-pcie",
> -		.suppress_bind_attrs = true,
>  		.of_match_table = qcom_pcie_match,
>  	},
>  };
> -builtin_platform_driver(qcom_pcie_driver);
> +module_platform_driver(qcom_pcie_driver);
> +
> +MODULE_AUTHOR("Stanimir Varbanov <svarbanov@...sol.com>");
> +MODULE_DESCRIPTION("Qualcomm PCIe root complex driver");
> +MODULE_LICENSE("GPL");
> -- 
> 2.35.1
>