Re: [PATCH RFC v6 7/7] mfd: ls2kbmc: Capture the reset event of BMC through GPIO

On Tue, 4 Aug 2026 21:14:25 +0200, Miao Wang via B4 Relay
<[email protected]> said:
> From: Miao Wang <[email protected]>
>
> The reset event of BMC is captured through GPIO. However, this driver
> bypasses the GPIO framework and directly accesses the GPIO controller
> through the fixed address. When the same GPIO controller is also
> exposed through ACPI and probed by the corresponding GPIO driver,
> there would be a conflict between the two drivers.
>
> This patch will try to find the GPIO through declared GPIO pin in the
> _CRS resources of the ACPI node. If no such delaration is found, the
> driver will fall back to search for the correct GPIO controller and pin
> according to the fixed address and pin number. A possible DSDT
> declaration for the GPIO pin might be as follows:
>
>     Device (BMC0) {
>         Name (_ADR, ...) // Match the PCI address of the BMC device
>         // \_SB.GPO1 is the ACPI path of the GPIO controller
>         Name (_CRS, ResourceTemplate () {
>             GpioInt (Edge, ActiveLow, Exclusive, PullNone, 0,
>                      "\\_SB.GPO1", 0) {
>                 14 // 14 is the GPIO pin number
>             }
>     }
>
> Signed-off-by: Miao Wang <[email protected]>
> ---
>  drivers/mfd/ls2k-bmc-core.c | 163 +++++++++++++++++++++++++++++++-------------
>  1 file changed, 116 insertions(+), 47 deletions(-)
>
> diff --git a/drivers/mfd/ls2k-bmc-core.c b/drivers/mfd/ls2k-bmc-core.c
> index e7bebfe696ac4554eb6283279811a27ed865ab73..97a666a136fe41ed4268cb70770201533aebb1d5 100644
> --- a/drivers/mfd/ls2k-bmc-core.c
> +++ b/drivers/mfd/ls2k-bmc-core.c
> @@ -26,6 +26,10 @@
>  #include <linux/stop_machine.h>
>  #include <linux/vt_kern.h>
>  #include <linux/console.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/gpio/driver.h>
> +#include <linux/gpio/property.h>
> +#include <linux/gpio/machine.h>
>
>  /* LS2K BMC resources */
>  #define LS2K_DISPLAY_RES_START		(SZ_16M + SZ_2M)
> @@ -81,18 +85,6 @@
>
>  #define PCI_REG_STRIDE			0x4
>
> -#define LS2K_BMC_RESET_GPIO		14
> -#define LOONGSON_GPIO_REG_BASE		0x1FE00500
> -#define LOONGSON_GPIO_REG_SIZE		0x18
> -#define LOONGSON_GPIO_OEN		0x0
> -#define LOONGSON_GPIO_FUNC		0x4
> -#define LOONGSON_GPIO_INTPOL		0x10
> -#define LOONGSON_GPIO_INTEN		0x14
> -
> -#define LOONGSON_IO_INT_BASE		16
> -#define LS2K_BMC_RESET_GPIO_INT_VEC	(LS2K_BMC_RESET_GPIO % 8)
> -#define LS2K_BMC_RESET_GPIO_GSI		(LOONGSON_IO_INT_BASE + LS2K_BMC_RESET_GPIO_INT_VEC)
> -
>  enum {
>  	LS2K_BMC_DISPLAY,
>  	LS2K_BMC_IPMI0,
> @@ -186,6 +178,7 @@ struct ls2k_bmc_ddata {
>  	struct work_struct bmc_reset_work;
>  	struct ls2k_bmc_pci_data bmc_pci_data;
>  	struct ls2k_bmc_bridge_pci_data bridge_pci_data;
> +	struct gpio_desc *reset_gpio;
>  };
>
>  static bool ls2k_bmc_bar0_addr_is_set(struct pci_dev *pdev)
> @@ -375,6 +368,91 @@ static void ls2k_bmc_save_pci_data(struct pci_dev *pdev, struct ls2k_bmc_ddata *
>  	pci_read_config_dword(pdev, PCI_INTERRUPT_LINE, &ddata->bmc_pci_data.interrupt_line);
>  }
>
> +static struct fwnode_handle *gpio_dev_get_fwnode(struct gpio_device *gdev)
> +{
> +	struct device *gdev_dev;
> +
> +	gdev_dev = gpio_device_to_device(gdev);
> +	return dev_fwnode(gdev_dev);

You can just do a one-liner:

	return dev_fwnode(gpio_device_to_device(gdev));

> +}
> +
> +static int ls2k_bmc_gpiochip_find(struct gpio_chip *gc, const void *data)
> +{
> +	struct acpi_device *adev;
> +	struct list_head resource_list;
> +	struct resource_entry *rentry;
> +	struct fwnode_handle *fwnode = gpio_dev_get_fwnode(gc->gpiodev);
> +	phys_addr_t start_addr = (phys_addr_t) data;
> +	int ret, found = 0;
> +
> +	if (!is_acpi_node(fwnode))
> +		goto out;
> +
> +	adev = to_acpi_device_node(fwnode);
> +	if (!adev)
> +		goto out;
> +
> +	INIT_LIST_HEAD(&resource_list);
> +
> +	ret = acpi_dev_get_memory_resources(adev, &resource_list);
> +	if (ret < 0)
> +		goto out;
> +	/*
> +	 * ACPI memory resources are ordered and only the first one is
> +	 * considered by the driver of the expected GPIO controller. So
> +	 * here we also only check the first one to see if it matches the
> +	 * expected address.
> +	 */
> +	rentry = list_first_entry_or_null(&resource_list, struct resource_entry, node);
> +	if (!rentry)
> +		goto free_resource_list;
> +	if (rentry->res->start == start_addr)
> +		found = 1;
> +
> +free_resource_list:
> +	acpi_dev_free_resource_list(&resource_list);
> +out:
> +	return found;
> +}
> +
> +static struct gpio_desc *ls2k_bmc_find_gpio(struct ls2k_bmc_ddata *ddata)
> +{
> +	/*
> +	 * In conventional way, the GPIO should be obtained through ACPI or
> +	 * device tree. However, when the information is not available,
> +	 * we should find the GPIO according to the convention of the server
> +	 * boards with LS2K BMC, the gpio signal reflecting the reset event
> +	 * of the BMC should be connected to pin 14 of the GPIO input of
> +	 * the first CPU node. The address of that GPIO controller is fixed.
> +	 */
> +	static const phys_addr_t LOONGSON_GPIO_REG_BASE = 0x1FE00500;
> +	static const unsigned int LS2K_BMC_RESET_GPIO = 14;
> +	int ret;
> +	struct gpio_device *gdev __free(gpio_device_put) = NULL;

Please declare the variable where you initialize it when using __free().

> +	struct property_entry ls2k_bmc_swnode_properties[2] = { 0 };

Prefer `= { };`.

> +
> +	dev_dbg(ddata->dev, "Searching for GPIO chip at address %pa\n", &LOONGSON_GPIO_REG_BASE);
> +
> +	gdev = gpio_device_find((void *)LOONGSON_GPIO_REG_BASE, ls2k_bmc_gpiochip_find);
> +

No need for a blank line here.

> +	if (!gdev) {
> +		dev_dbg(ddata->dev, "cannot find GPIO chip at address %pa, deferring\n",
> +			&LOONGSON_GPIO_REG_BASE);
> +		return ERR_PTR(-EPROBE_DEFER);
> +	}
> +
> +	ls2k_bmc_swnode_properties[0] = PROPERTY_ENTRY_GPIO("gpio",
> +		gpio_dev_get_fwnode(gdev), LS2K_BMC_RESET_GPIO, GPIO_ACTIVE_HIGH);

TBH this could become a GPIOLIB function as gpio_device_get_fwnode().

> +
> +	ret = device_create_managed_software_node(ddata->dev, ls2k_bmc_swnode_properties, NULL);
> +	if (ret) {
> +		dev_err(ddata->dev, "Failed to create software node for GPIO reset: %d\n", ret);
> +		return ERR_PTR(ret);

return dev_err_probe()? This can only be called from probe().

> +	}
> +
> +	return devm_gpiod_get_index(ddata->dev, NULL, 0, GPIOD_IN);
> +}
> +
>  static void ls2k_bmc_cancel_wq(void *data)
>  {
>  	struct ls2k_bmc_ddata *ddata = data;
> @@ -384,8 +462,7 @@ static void ls2k_bmc_cancel_wq(void *data)
>  static int ls2k_bmc_init(struct ls2k_bmc_ddata *ddata)
>  {
>  	struct pci_dev *pdev = to_pci_dev(ddata->dev);
> -	void __iomem *gpio_base;
> -	int gpio_irq, ret, val;
> +	int gpio_irq, ret;
>
>  	ls2k_bmc_save_pci_data(pdev, ddata);
>
> @@ -402,44 +479,36 @@ static int ls2k_bmc_init(struct ls2k_bmc_ddata *ddata)
>  		return ret;
>  	}
>
> -	gpio_base = ioremap(LOONGSON_GPIO_REG_BASE, LOONGSON_GPIO_REG_SIZE);
> -	if (!gpio_base)
> -		return -ENOMEM;
> -
> -	/* Disable GPIO output */
> -	val = readl(gpio_base + LOONGSON_GPIO_OEN);
> -	writel(val | BIT(LS2K_BMC_RESET_GPIO), gpio_base + LOONGSON_GPIO_OEN);
> -
> -	/* Enable GPIO functionality */
> -	val = readl(gpio_base + LOONGSON_GPIO_FUNC);
> -	writel(val & ~BIT(LS2K_BMC_RESET_GPIO), gpio_base + LOONGSON_GPIO_FUNC);
> -
> -	/* Set GPIO interrupts to low-level active */
> -	val = readl(gpio_base + LOONGSON_GPIO_INTPOL);
> -	writel(val & ~BIT(LS2K_BMC_RESET_GPIO), gpio_base + LOONGSON_GPIO_INTPOL);
> -
> -	/* Enable GPIO interrupts */
> -	val = readl(gpio_base + LOONGSON_GPIO_INTEN);
> -	writel(val | BIT(LS2K_BMC_RESET_GPIO), gpio_base + LOONGSON_GPIO_INTEN);
> +	ddata->reset_gpio = devm_gpiod_get_index_optional(&pdev->dev, NULL, 0, GPIOD_IN);
> +	if (IS_ERR(ddata->reset_gpio)) {
> +		ret = PTR_ERR(ddata->reset_gpio);
> +		ddata->reset_gpio = NULL;
> +		return dev_err_probe(ddata->dev, ret, "Failed to get GPIO pin for reset signal\n");
> +	}
> +	if (ddata->reset_gpio == NULL) {
> +		ddata->reset_gpio = ls2k_bmc_find_gpio(ddata);
> +		if (IS_ERR(ddata->reset_gpio)) {
> +			ret = PTR_ERR(ddata->reset_gpio);
> +			ddata->reset_gpio = NULL;
> +			return dev_err_probe(ddata->dev, ret,
> +					     "Failed to find GPIO pin for reset signal\n");

Why not just:

	return dev_err_probe(ddata->dev, PTR_ERR(ddata->reset_gpio), ...)?

> +		}
> +	}
>
> -	iounmap(gpio_base);
> +	gpio_irq = gpiod_to_irq(ddata->reset_gpio);
>
> -	/*
> -	 * Since gpio_chip->to_irq is not implemented in the Loongson-3 GPIO driver,
> -	 * acpi_register_gsi() is used to obtain the GPIO IRQ. The GPIO interrupt is a
> -	 * watchdog interrupt that is triggered when the BMC resets.
> -	 */
> -	gpio_irq = acpi_register_gsi(NULL, LS2K_BMC_RESET_GPIO_GSI, ACPI_EDGE_SENSITIVE,
> -				     ACPI_ACTIVE_LOW);
>  	if (gpio_irq < 0)
> -		return gpio_irq;
> +		return dev_err_probe(ddata->dev, gpio_irq,
> +				     "Failed to get IRQ for GPIO reset signal input\n");
>
> -	ret = devm_request_irq(ddata->dev, gpio_irq, ls2k_bmc_interrupt,
> -			       IRQF_SHARED | IRQF_TRIGGER_FALLING, "ls2kbmc gpio", ddata);
> -	if (ret)
> -		dev_err(ddata->dev, "Failed to request LS2KBMC GPIO IRQ %d.\n", gpio_irq);
> +	ret = devm_request_irq(&pdev->dev, gpio_irq, ls2k_bmc_interrupt,
> +			       IRQF_SHARED | IRQF_TRIGGER_FALLING, "ls2kbmc reset", ddata);
> +
> +	if (ret != 0)
> +		return dev_err_probe(ddata->dev, ret,
> +				     "Failed to request IRQ %d for GPIO reset signal input.\n",
> +				     gpio_irq);
>
> -	acpi_unregister_gsi(LS2K_BMC_RESET_GPIO_GSI);
>  	return ret;
>  }
>
>
> --
> 2.49.0
>
>
>


Obviously this is ugly but I understand the need for this workaround so with
the issues above addressed, this will work for me.

Bart