linux-kernel - Re: [PATCH] leds: add SGI IP30 led support

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Date:   Thu, 16 Jan 2020 09:21:59 -0600
From:   Dan Murphy <dmurphy@...com>
To:     Thomas Bogendoerfer <tbogendoerfer@...e.de>
CC:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>, <linux-kernel@...r.kernel.org>,
        <linux-leds@...r.kernel.org>
Subject: Re: [PATCH] leds: add SGI IP30 led support

Thomas

On 1/16/20 5:05 AM, Thomas Bogendoerfer wrote:
> On Wed, 15 Jan 2020 07:46:13 -0600
> Dan Murphy <dmurphy@...com> wrote:
>
>> Thomas
>>
>> On 1/15/20 7:05 AM, Thomas Bogendoerfer wrote:
>>> This patch implemenets a driver to support the front panel LEDs of
>>> SGI Octane (IP30) workstations.
>> Thanks for the patch
>>
>> Some nitpicks below
>>
>>
>>> Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@...e.de>
>>> ---
>>>    drivers/leds/Kconfig     | 11 ++++++
>>>    drivers/leds/Makefile    |  1 +
>>>    drivers/leds/leds-ip30.c | 82 ++++++++++++++++++++++++++++++++++++++++
>>>    3 files changed, 94 insertions(+)
>>>    create mode 100644 drivers/leds/leds-ip30.c
>>>
>>> diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
>>> index 4b68520ac251..8ef0fe900928 100644
>>> --- a/drivers/leds/Kconfig
>>> +++ b/drivers/leds/Kconfig
>>> @@ -836,6 +836,17 @@ config LEDS_LM36274
>>>    	  Say Y to enable the LM36274 LED driver for TI LMU devices.
>>>    	  This supports the LED device LM36274.
>>>    
>>> +config LEDS_IP30
>>> +	tristate "LED support for SGI Octane machines"
>>> +	depends on LEDS_CLASS
>>> +	depends on SGI_MFD_IOC3
>> What is the dependency on the MFD?
> the gpio lines where the leds are connected are managed by the mfd ioc3 driver.
> So without that driver this led driver will not be started.
Ack
>
>>> +
>>> +
>>> +	if (num == 0) {
>>> +		data->cdev.name = "ip30:white";
>> This also needs a function as defined in dt-bindings/common.h
>>> +		data->cdev.default_trigger = "default-on";
>> The name, color, function and trigger can be pulled from the DT or Firmware.
>>
>> The firmware should contain a node for each LED to be configured.
> SGI Octanes don't have DT and the firmware just toggles some of the leds,
> but doesn't provide informations about it. That's why this is hardcoded
> in the driver. The MFD driver detects the ioc3 chip and knows it's a
> SGI Octane mainboard and creates the led platform device.
>
> How is the correct way to this without DT ?

Please refer to the leds-class document (1) under LED device naming 
convention

If you don't have a DT then set the name accordingly.  The functions are 
defined in the common.h and the colors are exported in the leds-class driver


1 https://www.kernel.org/doc/Documentation/leds/leds-class.rst

>
>>> +	} else {
>>> +		data->cdev.name = "ip30:red";
>> Same as above
>>> +		data->cdev.default_trigger = "panic";
>>> +		writel(0, data->reg);
>> Is the LED on by default?
> Depends on the hardware state. If PROM firmware detects some hardware issues,
> it turns on the red LED. Otherwise it's off.

So why would we turn it off if the PROM FW turned it on?

Dan