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Date:	Fri, 8 Aug 2014 16:36:55 +0200
From:	Wim Van Sebroeck <wim@...ana.be>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	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 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.

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