linux-kernel - Re: [PATCH 1/5] mfd: add Congatec Board Controller mfd driver

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Message-ID: <618cb281-9fec-471f-9e3d-c7a471f75a7a@bootlin.com>
Date: Fri, 13 Sep 2024 10:30:20 +0200
From: Thomas Richard <thomas.richard@...tlin.com>
To: Lee Jones <lee@...nel.org>
Cc: Linus Walleij <linus.walleij@...aro.org>,
 Bartosz Golaszewski <brgl@...ev.pl>, Andi Shyti <andi.shyti@...nel.org>,
 Wim Van Sebroeck <wim@...ux-watchdog.org>, Guenter Roeck
 <linux@...ck-us.net>, linux-kernel@...r.kernel.org,
 linux-gpio@...r.kernel.org, linux-i2c@...r.kernel.org,
 linux-watchdog@...r.kernel.org, thomas.petazzoni@...tlin.com,
 blake.vermeer@...sight.com
Subject: Re: [PATCH 1/5] mfd: add Congatec Board Controller mfd driver

On 9/12/24 16:13, Lee Jones wrote:
> On Tue, 10 Sep 2024, Thomas Richard wrote:
> 
>> On 8/22/24 12:38, Lee Jones wrote:
>>> On Fri, 09 Aug 2024, Thomas Richard wrote:
>>>
>>>> Add core MFD driver for the Board Controller found on some Congatec SMARC
>>>> module. This Board Controller provides functions like watchdog, GPIO, and
>>>> I2C busses.
>>>>
>>>> This commit add support only for the conga-SA7 module.
>>>>
>>>> Signed-off-by: Thomas Richard <thomas.richard@...tlin.com>
>>>> ---
>>>>  drivers/mfd/Kconfig      |  12 ++
>>>>  drivers/mfd/Makefile     |   1 +
>>>>  drivers/mfd/cgbc-core.c  | 453 +++++++++++++++++++++++++++++++++++++++++++++++
>>>>  include/linux/mfd/cgbc.h |  44 +++++
>>>>  4 files changed, 510 insertions(+)
>>>>
>>>> diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
>>>> index bc8be2e593b6..3e0530f30267 100644
>>>> --- a/drivers/mfd/Kconfig
>>>> +++ b/drivers/mfd/Kconfig
>>>> @@ -224,6 +224,18 @@ config MFD_AXP20X_RSB
>>>>  	  components like regulators or the PEK (Power Enable Key) under the
>>>>  	  corresponding menus.
>>>>  
>>>> +config MFD_CGBC
>>>> +	tristate "Congatec Board Controller"
>>>> +	select MFD_CORE
>>>> +	depends on X86
>>>> +	help
>>>> +	  This is the core driver of the Board Controller found on some Congatec
>>>> +	  SMARC modules. The Board Controller provides functions like watchdog,
>>>> +	  I2C busses, and GPIO controller.
>>>> +
>>>> +	  To compile this driver as a module, choose M here: the module will be
>>>> +	  called cgbc-core.
>>>> +
>>>>  config MFD_CROS_EC_DEV
>>>>  	tristate "ChromeOS Embedded Controller multifunction device"
>>>>  	select MFD_CORE
>>>> diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
>>>> index 02b651cd7535..d5da3fcd691c 100644
>>>> --- a/drivers/mfd/Makefile
>>>> +++ b/drivers/mfd/Makefile
>>>> @@ -13,6 +13,7 @@ obj-$(CONFIG_MFD_SM501)		+= sm501.o
>>>>  obj-$(CONFIG_ARCH_BCM2835)	+= bcm2835-pm.o
>>>>  obj-$(CONFIG_MFD_BCM590XX)	+= bcm590xx.o
>>>>  obj-$(CONFIG_MFD_BD9571MWV)	+= bd9571mwv.o
>>>> +obj-$(CONFIG_MFD_CGBC)		+= cgbc-core.o
>>>>  obj-$(CONFIG_MFD_CROS_EC_DEV)	+= cros_ec_dev.o
>>>>  obj-$(CONFIG_MFD_CS42L43)	+= cs42l43.o
>>>>  obj-$(CONFIG_MFD_CS42L43_I2C)	+= cs42l43-i2c.o
>>>> diff --git a/drivers/mfd/cgbc-core.c b/drivers/mfd/cgbc-core.c
>>>> new file mode 100644
>>>> index 000000000000..cca9b1170cc9
>>>> --- /dev/null
>>>> +++ b/drivers/mfd/cgbc-core.c
>>>> @@ -0,0 +1,453 @@
>>>> +// SPDX-License-Identifier: GPL-2.0-or-later
>>>> +/*
>>>> + * Congatec Board Controller MFD core driver.
>>>
>>> No such thing as an MFD.
>>
>> What should it be if it's not an MFD ?
> 
> You should be telling me this. :)
> 
> "Board Controller" according to the Kconfig entry.
> 

This Congatec Board Controller is an external micro-controller that is
interfaced with the CPU through a eSPI bus.
This Board Controller provides multiple functions: an I2C controller, a
GPIO controller, a watchdog and other not yet implemented functions
(temp/voltage sensors, backlight).

Therefore, the MFD subsystem is a very good fit, as it allows to have a
core driver that implements the communication with the external
micro-controller, and then individual drivers for each of the functions
offered by this Board Controller.

Thomas