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

[Miao Wang <shankerwangmiao@gmail.com>]

Hi,

> 2026年7月8日 21:14，Xi Ruoyao <xry111@xry111.site> 写道：
> 
> On Wed, 2026-07-08 at 05:16 +0800, Miao Wang via B4 Relay wrote:
>> From: Miao Wang <shankerwangmiao@gmail.com>
>> 
>> 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.

Yes, it is a proposal. GpioInt() in the _CRS() should be at least
required to associate the BMC device to the GPIO pin. Having a _DSD
might be better to label the gpio pin with human readable label. I
however don't think _DSD is important because there is only one pin
needed, and devm_gpiod_get_index can be used to obtain the gpio line
description using the index in _CRS()

> 
> 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";

I'll further look into whether swnode can be used.

>  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.

I'm open with such discussions.

Cheers,

Miao Wang