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

[Simon Guinot]

On Wed, Feb 25, 2015 at 06:31:09AM -0800, Guenter Roeck wrote:
> 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 <simon.guinot at sequanux.org>
> >>>>>---
> >>>>>  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.

Well, I think we are interested in both the interrupt signal _and_ the
GPIO value. We need to display the later through the sysfs fan1_alarm
file.

Using the irq field from struct i2c_client is quite handy but the GPIO
polarity information is lost...

That's why I think we should probably use a dedicated property.

> 
> >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.

It was a question. I was not knowing the proper way for a driver to
connect with this interrupt. Thanks for the explanation.

> 
> >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.

Considering we will have to read this GPIO, then we will have this
dependency.

Simon
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 181 bytes
Desc: Digital signature
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20150225/bcc20b7c/attachment.sig>