Re: [PATCH RFC v2 7/7] mfd: ls2kbmc: Capture the reset event of BMC through GPIO

[Xi Ruoyao]

On Wed, 2026-07-08 at 05:16 +0800, Miao Wang via B4 Relay wrote:
> From: Miao Wang <shankerwangmiao@xxxxxxxxx>
> 
> 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
>             }
>     }

I think this is a proposal without real implementation yet?  If so...

/* snip */

> +	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;
> +	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);

... consider adding a _DSD method to label (like "bmc-reset") the GPIO
for the proposed BMC0 device so you can use devm_gpiod_get to get the
GPIO, instead of using the hand-brew code to parse the ACPI node. 
See https://www.kernel.org/doc/html/latest/firmware-guide/acpi/gpio-properties.html.

Combining this with Bartosz's comment, the logic would be like:

  if (missing the ACPI node)
    assign a swnode to label "gpio14" as "bmc-reset";

  gpio_desc = devm_gpiod_get(&dev, "bmc-reset", GPIOD_IN);

And such a proposal will need to be discussed with Loongson.  Yes I know
people may hate the "control" from the vendor, but having some
effectively dead code (i.e. supporting some non-exist firmware) in the
kernel is worse.


-- 
Xi Ruoyao <xry111@xxxxxxxxxxx>