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Date:	Fri, 8 Aug 2014 09:49:39 +0200
From:	Andreas Werner <andreas.werner@....de>
To:	Guenter Roeck <linux@...ck-us.net>
CC:	Andreas Werner <andreas.werner@....de>,
	Wim Van Sebroeck <wim@...ana.be>,
	Bryan Wu <cooloney@...il.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>,
	"rpurdie@...ys.net" <rpurdie@...ys.net>,
	Linux LED Subsystem <linux-leds@...r.kernel.org>,
	<linux-watchdog@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] drivers/leds/leds-menf21bmc: introduce MEN
 14F021P00 BMC LED driver

On Wed, Jul 30, 2014 at 06:57:46AM -0700, Guenter Roeck wrote:
> On 07/30/2014 01:08 AM, Andreas Werner wrote:
> >On Tue, Jul 29, 2014 at 02:47:08PM -0700, Guenter Roeck wrote:
> >>On 07/29/2014 02:12 PM, Wim Van Sebroeck wrote:
> >>>Hi Andreas,
> >>>
> >>>>aOn Thu, Jul 24, 2014 at 03:00:09PM -0700, Bryan Wu wrote:
> >>>>>On Thu, Jul 17, 2014 at 6:18 AM, Andreas Werner <andreas.werner@....de> wrote:
> >>>>>>Added driver to support the 14F021P00 BMC LEDs.
> >>>>>>The BMC is a Board Management Controll include four LEDs which
> >>>>>>can be switched on and off.
> >>>>>>
> >>>>>>This driver use the I2C interface to the BMC using the menf21bmc MFD Core driver.
> >>>>>>
> >>>>>>Signed-off-by: Andreas Werner <andreas.werner@....de>
> >>>>>>---
> >>>>>>  drivers/leds/Kconfig          |   6 ++
> >>>>>>  drivers/leds/Makefile         |   1 +
> >>>>>>  drivers/leds/leds-menf21bmc.c | 134 ++++++++++++++++++++++++++++++++++++++++++
> >>>>>>  3 files changed, 141 insertions(+)
> >>>>>>  create mode 100644 drivers/leds/leds-menf21bmc.c
> >>>>>>
> >>>>>>diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
> >>>>>>index 27cf0cd..d38ff3f 100644
> >>>>>>--- a/drivers/leds/Kconfig
> >>>>>>+++ b/drivers/leds/Kconfig
> >>>>>>@@ -458,6 +458,12 @@ config LEDS_OT200
> >>>>>>           This option enables support for the LEDs on the Bachmann OT200.
> >>>>>>           Say Y to enable LEDs on the Bachmann OT200.
> >>>>>>
> >>>>>>+config LEDS_MENF21BMC
> >>>>>>+       tristate "LED support for the MEN 14F021P00 BMC"
> >>>>>>+       depends on LEDS_CLASS && MFD_MENF21BMC
> >>>>>
> >>>>>I think it also depends on I2C.
> >>>>
> >>>>Yes you are right.
> >>>>
> >>>>>
> >>>>>>+       help
> >>>>>>+         Say Y here to include support for the MEN 14F021P00 BMC LEDs.
> >>>>>>+
> >>>>>>  comment "LED driver for blink(1) USB RGB LED is under Special HID drivers (HID_THINGM)"
> >>>>>>
> >>>>>>  config LEDS_BLINKM
> >>>>>>diff --git a/drivers/leds/Makefile b/drivers/leds/Makefile
> >>>>>>index 3c03666..cadc433 100644
> >>>>>>--- a/drivers/leds/Makefile
> >>>>>>+++ b/drivers/leds/Makefile
> >>>>>>@@ -53,6 +53,7 @@ obj-$(CONFIG_LEDS_MAX8997)            += leds-max8997.o
> >>>>>>  obj-$(CONFIG_LEDS_LM355x)              += leds-lm355x.o
> >>>>>>  obj-$(CONFIG_LEDS_BLINKM)              += leds-blinkm.o
> >>>>>>  obj-$(CONFIG_LEDS_VERSATILE)           += leds-versatile.o
> >>>>>>+obj-$(CONFIG_LEDS_MENF21BMC)           += leds-menf21bmc.o
> >>>>>>
> >>>>>>  # LED SPI Drivers
> >>>>>>  obj-$(CONFIG_LEDS_DAC124S085)          += leds-dac124s085.o
> >>>>>>diff --git a/drivers/leds/leds-menf21bmc.c b/drivers/leds/leds-menf21bmc.c
> >>>>>>new file mode 100644
> >>>>>>index 0000000..5eaa119
> >>>>>>--- /dev/null
> >>>>>>+++ b/drivers/leds/leds-menf21bmc.c
> >>>>>>@@ -0,0 +1,134 @@
> >>>>>>+/*
> >>>>>>+ *  MEN 14F021P00 Board Management Controller (BMC) LEDs Driver.
> >>>>>>+ *
> >>>>>>+ *  This is the core LED driver of the MEN 14F021P00 BMC.
> >>>>>>+ *  There are four LEDs available which can be switched on and off.
> >>>>>>+ *  STATUS LED, HOT SWAP LED, USER LED 1, USER LED 2
> >>>>>>+ *
> >>>>>>+ *  Copyright (C) 2014 MEN Mikro Elektronik Nuernberg GmbH
> >>>>>>+ *  Author: Andreas Werner <andreas.werner@....de>
> >>>>>>+ *  All rights reserved.
> >>>>>>+ *
> >>>>>>+ *  This program is free software; you can redistribute  it and/or modify it
> >>>>>>+ *  under  the terms of  the GNU General  Public License as published by the
> >>>>>>+ *  Free Software Foundation;  either version 2 of the  License, or (at your
> >>>>>>+ *  option) any later version.
> >>>>>>+ *
> >>>>>>+ */
> >>>>>>+
> >>>>>>+#include <linux/module.h>
> >>>>>>+#include <linux/kernel.h>
> >>>>>>+#include <linux/platform_device.h>
> >>>>>>+#include <linux/leds.h>
> >>>>>>+#include <linux/i2c.h>
> >>>>>>+
> >>>>>>+#define BMC_CMD_LED_GET_SET    0xA0
> >>>>>>+#define BMC_BIT_LED_STATUS     BIT(0)
> >>>>>>+#define BMC_BIT_LED_HOTSWAP    BIT(1)
> >>>>>>+#define BMC_BIT_LED_USER1      BIT(2)
> >>>>>>+#define BMC_BIT_LED_USER2      BIT(3)
> >>>>>>+
> >>>>>>+struct menf21bmc_led {
> >>>>>>+       struct led_classdev cdev;
> >>>>>>+       u8 led_bit;
> >>>>>>+       const char *name;
> >>>>>>+       struct i2c_client *i2c_client;
> >>>>>>+};
> >>>>>>+
> >>>>>>+static struct menf21bmc_led leds[] = {
> >>>>>>+       {
> >>>>>>+               .name = "menf21bmc:led_status",
> >>>>>>+               .led_bit = BMC_BIT_LED_STATUS,
> >>>>>>+       },
> >>>>>>+       {
> >>>>>>+               .name = "menf21bmc:led_hotswap",
> >>>>>>+               .led_bit = BMC_BIT_LED_HOTSWAP,
> >>>>>>+       },
> >>>>>>+       {
> >>>>>>+               .name = "menf21bmc:led_user1",
> >>>>>>+               .led_bit = BMC_BIT_LED_USER1,
> >>>>>>+       },
> >>>>>>+       {
> >>>>>>+               .name = "menf21bmc:led_user2",
> >>>>>>+               .led_bit = BMC_BIT_LED_USER2,
> >>>>>>+       }
> >>>>>>+};
> >>>>>>+
> >>>>>>+static DEFINE_MUTEX(led_lock);
> >>>>>>+
> >>>>>>+static void
> >>>>>>+menf21bmc_led_set(struct led_classdev *led_cdev, enum led_brightness value)
> >>>>>>+{
> >>>>>>+       int led_val;
> >>>>>>+       struct menf21bmc_led *led = container_of(led_cdev,
> >>>>>>+                                       struct menf21bmc_led, cdev);
> >>>>>>+
> >>>>>>+       mutex_lock(&led_lock);
> >>>>>>+       led_val = i2c_smbus_read_byte_data(led->i2c_client,
> >>>>>>+                                               BMC_CMD_LED_GET_SET);
> >>>>>>+       if (led_val < 0)
> >>>>>>+               goto err_out;
> >>>>>>+
> >>>>>>+       if (value == LED_OFF)
> >>>>>>+               led_val &= ~led->led_bit;
> >>>>>>+       else
> >>>>>>+               led_val |= led->led_bit;
> >>>>>>+
> >>>>>>+       i2c_smbus_write_byte_data(led->i2c_client,
> >>>>>>+                                       BMC_CMD_LED_GET_SET, led_val);
> >>>>>>+err_out:
> >>>>>>+       mutex_unlock(&led_lock);
> >>>>>>+}
> >>>>>>+
> >>>>>>+static int menf21bmc_led_probe(struct platform_device *pdev)
> >>>>>>+{
> >>>>>>+       int i;
> >>>>>>+       int ret;
> >>>>>>+       struct i2c_client *i2c_client = to_i2c_client(pdev->dev.parent);
> >>>>>>+
> >>>>>>+       for (i = 0; i < ARRAY_SIZE(leds); i++) {
> >>>>>>+               leds[i].cdev.name = leds[i].name;
> >>>>>>+               leds[i].cdev.brightness_set = menf21bmc_led_set;
> >>>>>>+               leds[i].i2c_client = i2c_client;
> >>>>>>+               ret = led_classdev_register(&pdev->dev, &leds[i].cdev);
> >>>>>>+               if (ret < 0)
> >>>>>>+                       goto err_free_leds;
> >>>>>>+       }
> >>>>>>+       dev_info(&pdev->dev, "MEN 140F21P00 BMC LED device enabled\n");
> >>>>>>+
> >>>>>>+       return 0;
> >>>>>>+
> >>>>>>+err_free_leds:
> >>>>>>+       dev_err(&pdev->dev, "failed to register LED device\n");
> >>>>>>+
> >>>>>>+       for (i = i - 1; i >= 0; i--)
> >>>>>>+               led_classdev_unregister(&leds[i].cdev);
> >>>>>>+
> >>>>>>+       return ret;
> >>>>>>+}
> >>>>>>+
> >>>>>>+static int menf21bmc_led_remove(struct platform_device *pdev)
> >>>>>>+{
> >>>>>>+       int i;
> >>>>>>+
> >>>>>>+       for (i = 0; i < ARRAY_SIZE(leds); i++)
> >>>>>>+               led_classdev_unregister(&leds[i].cdev);
> >>>>>>+
> >>>>>>+       return 0;
> >>>>>>+}
> >>>>>>+
> >>>>>>+static struct platform_driver menf21bmc_led = {
> >>>>>>+       .probe          = menf21bmc_led_probe,
> >>>>>>+       .remove         = menf21bmc_led_remove,
> >>>>>>+       .driver         = {
> >>>>>>+               .name           = "menf21bmc_led",
> >>>>>>+               .owner          = THIS_MODULE,
> >>>>>>+       },
> >>>>>>+};
> >>>>>>+
> >>>>>
> >>>>>This is not a normal platform driver, it should be a I2C driver.
> >>>>>
> >>>>>>+module_platform_driver(menf21bmc_led);
> >>>>>
> >>>>>So please move to use module_i2c_driver.
> >>>>
> >>>>Ok, but then I have to change that in the watchdog driver too, which
> >>>>is quite the same as here.
> >>>>
> >>>>Lee, Guenther what do you think regarding the watchdog driver?
> >>>
> >>>If the watchdog part is indeed also i2c alike device then the watchdog part should also be an i2c driver...
> >>>
> >>
> >>Isn't this all the same chip ? If so, there should be only one i2c driver.
> >>Unless the i2c access is too complicated, it might make sense to use regmap
> >>to access the chip, and pass the regmap pointer to the mfd slave drivers
> >>to handle the actual communication with the chip.
> >>
> >>Guenter
> >>
> >
> >Yes this is all the same chip which has different features like LEDs and Watchdog.
> >This is why the mfd is the i2c_driver which instantiates the slave devices which
> >are platform drivers.
> >
> >Is that not the normal way to handle those device?
> >Is it really necessary to handle this to regmap?
> >
> 
> Not really sure if 'necessary' is the right term, it is just convenient.
> Regmap takes care of register caching, for example, so you would not have to
> re-read register values again and again from the chip just to modify a bit
> of a register.
> You can pass the regmap pointer in the platform data, or you can pass the
> pointer to the i2c client. Using regmap makes the client driver independent
> of the i2c subsystem. The one thing you can _not_ do is to declare the client
> drivers to be i2c drivers.
> 
> Guenter
> 
I've checked out the regmap and it really sounds good.
Before I will made those changes which is almost a complete replacement
of the interface, i would like to know exactly why the slaves are no platform 
devices.

For now I think the implementation of the menf21bmc using an mfd as the i2c_driver
and the slaves as platform devices is correct.
Regmap would be just another type of interfaces which I could use.

Please correct me if I'm'wrong.

Regards
Andy
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