Subject: [PATCH] ARM: Kirkwood: enable GPIO fan alarm support for 2Big Network v2

From: [email-masked] (Guenter Roeck)
Date: Wed, 25 Feb 2015 06:31:09 -0800

On 02/25/2015 04:36 AM, Simon Guinot wrote:
> On Mon, Feb 23, 2015 at 06:49:50AM -0800, Guenter Roeck wrote:
>> On 02/23/2015 06:40 AM, Simon Guinot wrote:
>>> On Mon, Feb 23, 2015 at 06:10:59AM -0800, Guenter Roeck wrote:
>>>> On 02/23/2015 05:02 AM, Simon Guinot wrote:
>>>>> On the LaCie 2Big Network v2 (net2big_v2) board, the fan alarm is not
>>>>> wired to the I2C fan controller but to a separe GPIO. This GPIO can be
>>>>> controlled by using the gpio-fan driver.
>>>>>
>>>>> This patch adds the gpio-fan alarm description in the net2big_v2 DTS.
>>>>>
>>>>> Signed-off-by: Simon Guinot <[email-masked]>
>>>>> ---
>>>>>   arch/arm/boot/dts/kirkwood-net2big.dts | 5 +++++
>>>>>   1 file changed, 5 insertions(+)
>>>>>
>>>>> diff --git a/arch/arm/boot/dts/kirkwood-net2big.dts b/arch/arm/boot/dts/kirkwood-net2big.dts
>>>>> index 53dc37a3b687..e4f7e497379f 100644
>>>>> --- a/arch/arm/boot/dts/kirkwood-net2big.dts
>>>>> +++ b/arch/arm/boot/dts/kirkwood-net2big.dts
>>>>> @@ -27,6 +27,11 @@
>>>>>   		device_type = "memory";
>>>>>   		reg = <0x00000000 0x10000000>;
>>>>>   	};
>>>>> +
>>>>> +	gpio_fan {
>>>>> +		compatible = "gpio-fan";
>>>>> +		alarm-gpios = <&gpio0 25 GPIO_ACTIVE_LOW>;
>>>>> +	};
>>>>>   };
>>>>>
>>>>>   &regulators {
>>>>>
>>>> Again, wrong solution, and conceptually wrong as well from a dt perspective.
>>>>
>>>> The alarm signal should be handled by the g762 driver, and the alarm-gpios
>>>> property should be added to the g762 description.
>>>
>>> OK. Then you think it would be better to add support for alarm GPIOs
>>> support in the g762. The problem is that we should have to find a
>>> generic way to do that. After all, we could want the very same
>>> modification for a bunch of fan drivers.
>>>
>> Can't help it. After all, the interrupt handling logic is different for each chip,
>> and there are non-DT systems out there.
>>
>> The g762 property should probably be something like
>>
>> 	g762 at 3e {
>>                  compatible = "gmt,g762";
>>                  reg = <0x3e>;
>>                  clocks = <&g762_clk>;
>> 		interrupt-parent = <&gpio0>;
>> 		interrupts = <25 GPIO_ACTIVE_LOW>;
>>          };
>>
>> struct i2c_client has an irq field, and as far as I can see it is filled in
>> automatically from the dt node. So all the driver should have to do is to
>> implement an interrupt handler.
>
> Is that OK to pass a GPIO line through the "interrupts" property ?

Why not ? That is how it is supposed to be used. The driver neither needs
to know nor should know that its interrupt line is connected to a gpio pin.

> Moreover it seems to me that g763 controller (compatible) supports
> alert interrupts through SMBus. Then maybe we should save the
> "interrupts" property for this signal ?
>
You lost me there. The SMBus alert signal is shared among multiple chips.
If a system supports it, it should be connected to the alert interrupt handler
(in i2c-smbus.c), which would handle it and pass it to a driver's alert function.

> Don't you think it would be more explicit to have a separate DT
> property (such as "gpio-alarm") and also a dedicated field in the
> g762 platform data structure ?
>

No. It would add an unnecessary dependency on gpio (or, rather, gpio
driven interrupts) to the g762 driver, and it would limit its usability.

Guenter