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Date:	Mon, 11 Aug 2014 10:19:49 +0200
From:	Andreas Werner <andreas.werner@....de>
To:	Wim Van Sebroeck <wim@...ana.be>
CC:	Guenter Roeck <linux@...ck-us.net>,
	Andreas Werner <andreas.werner@....de>,
	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 Fri, Aug 08, 2014 at 04:36:55PM +0200, Wim Van Sebroeck wrote:
> > On 08/08/2014 12:49 AM, Andreas Werner wrote:
> > >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.
> > >
> > Did I say that ?
> 
> What we wanted to say was:
> 1) if your multifunctional device is working as entity's of its own and these "standalone" devices are an i2c device then they should be configured as a i2c device driver.
> 2) is the multifunctional device has different functionality (like watchdog, gpio, ...) and it works as a block (thus there are overlaps) and you have no clean i2c or pci or usb boundaries then you normally use platform device drivers.
> 
> Apart from that it would in this case also be nice to use the regmap api.
> 
> Sorry that it got "complicated".
> 
> Kind regards,
> Wim.
> 

The chip is like you described in 2). This is why the slaves are platform device.
It is not "complicated" it was just a little confuse.
Thanks for the nice explanation.

Next time if i develope a driver like this, i will use regmap but for the bmc i
will let it as it is.

I will send a v4 with the little remarks from your guys, in the next days.

Thanks.

Regards
Andy

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