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 19:36，Bartosz Golaszewski <brgl@kernel.org> 写道：
> 
> On Tue, 7 Jul 2026 23:16:31 +0200, Miao Wang via B4 Relay
> <devnull+shankerwangmiao.gmail.com@kernel.org> said:
>> 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
>>            }
>>    }
>> 
>> Signed-off-by: Miao Wang <shankerwangmiao@gmail.com>
>> ---
>> drivers/mfd/ls2k-bmc-core.c | 162 +++++++++++++++++++++++++++++++-------------
>> 1 file changed, 115 insertions(+), 47 deletions(-)
>> 
>> diff --git a/drivers/mfd/ls2k-bmc-core.c b/drivers/mfd/ls2k-bmc-core.c
>> index f87224105b3720cca97dcef089dad63fe57bc8c2..7187b2dfddc3acfb9fdf3cb3b4675299928dd03a 100644
>> --- a/drivers/mfd/ls2k-bmc-core.c
>> +++ b/drivers/mfd/ls2k-bmc-core.c
>> @@ -26,6 +26,9 @@
>> #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.h>
> 
> I've stopped here because this is a legacy header that must not be included
> and none of the interfaces in it must be used, as per the - very loud - comment
> at the top of that file.

I fully understand using the legacy interface is deprecated. However, there
seems no other way to obtain a gpio line description after a gpio device
is found using gpio_device_find(). As the comment shows in the code below,
the only place I use the legacy interface is:

gdev = gpio_device_find(...);
desc = gpio_device_get_desc(gdev, LS2K_BMC_RESET_GPIO);

// XXX: might be better to use gpiod_request()
legacy_gpio = desc_to_gpio(desc);
devm_gpio_request_one(..., legacy_gpio, ...);
return gpio_to_desc(legacy_gpio);

I just borrowed the legacy gpio interface to request the irq description. I
think that gpiod_request() should be better to be used here, but it is not
an interface that is exposed. As a result, I post this patch as a PoC here
to discuss and find a better way to achieve this.

Cheers,

Miao Wang