linux-kernel - Re: [PATCH v2 2/2] mfd: ene-kb3930: Add driver for ENE KB3930 Embedded Controller

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Message-ID: <20200519104933.GX271301@dell>
Date:   Tue, 19 May 2020 11:49:33 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Lubomir Rintel <lkundrak@...sk>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mfd: ene-kb3930: Add driver for ENE KB3930
 Embedded Controller

On Mon, 04 May 2020, Lubomir Rintel wrote:

> Hi,
> 
> thanks for your review. There are some inline responses below. Where I'm not
> responding it means that I'll be just fixing what you've pointed out.
> 
> On Wed, Apr 29, 2020 at 07:00:37AM +0100, Lee Jones wrote:
> > On Sat, 25 Apr 2020, Lubomir Rintel wrote:
> > 
> > > This driver provides access to the EC RAM of said embedded controller
> > > attached to the I2C bus as well as optionally supporting its slightly weird
> > > power-off/restart protocol.
> > > 
> > > A particular implementation of the EC firmware can be identified by a
> > > model byte. If this driver identifies the Dell Ariel platform, it
> > > registers the appropriate cells.
> > > 
> > > Signed-off-by: Lubomir Rintel <lkundrak@...sk>
> > > ---
> > >  drivers/mfd/Kconfig      |  10 ++
> > >  drivers/mfd/Makefile     |   1 +
> > >  drivers/mfd/ene-kb3930.c | 209 +++++++++++++++++++++++++++++++++++++++
> > >  3 files changed, 220 insertions(+)
> > >  create mode 100644 drivers/mfd/ene-kb3930.c
> > > 
> > > diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
> > > index 0a59249198d3..dae18a2beab5 100644
> > > --- a/drivers/mfd/Kconfig
> > > +++ b/drivers/mfd/Kconfig
> > > @@ -398,6 +398,16 @@ config MFD_DLN2
> > >  	  etc. must be enabled in order to use the functionality of
> > >  	  the device.
> > >  
> > > +config MFD_ENE_KB3930
> > > +	tristate "ENE KB3930 Embedded Controller support"
> > > +	depends on I2C
> > > +	depends on MACH_MMP3_DT || COMPILE_TEST
> > > +	select MFD_CORE
> > > +	help
> > > +	  This adds support for accessing the registers on ENE KB3930, Embedded
> > > +	  Controller. Additional drivers such as LEDS_ARIEL must be enabled in
> > > +	  order to use the functionality of the device.
> > > +
> > >  config MFD_EXYNOS_LPASS
> > >  	tristate "Samsung Exynos SoC Low Power Audio Subsystem"
> > >  	depends on ARCH_EXYNOS || COMPILE_TEST
> > > diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
> > > index f935d10cbf0f..2d2f5bc12841 100644
> > > --- a/drivers/mfd/Makefile
> > > +++ b/drivers/mfd/Makefile
> > > @@ -14,6 +14,7 @@ obj-$(CONFIG_ARCH_BCM2835)	+= bcm2835-pm.o
> > >  obj-$(CONFIG_MFD_BCM590XX)	+= bcm590xx.o
> > >  obj-$(CONFIG_MFD_BD9571MWV)	+= bd9571mwv.o
> > >  obj-$(CONFIG_MFD_CROS_EC_DEV)	+= cros_ec_dev.o
> > > +obj-$(CONFIG_MFD_ENE_KB3930)	+= ene-kb3930.o
> > >  obj-$(CONFIG_MFD_EXYNOS_LPASS)	+= exynos-lpass.o
> > >  
> > >  obj-$(CONFIG_HTC_PASIC3)	+= htc-pasic3.o
> > > diff --git a/drivers/mfd/ene-kb3930.c b/drivers/mfd/ene-kb3930.c
> > > new file mode 100644
> > > index 000000000000..1123f3a1c816
> > > --- /dev/null
> > > +++ b/drivers/mfd/ene-kb3930.c
> > > @@ -0,0 +1,209 @@
> > > +// SPDX-License-Identifier: BSD-2-Clause OR GPL-2.0-or-later
> > > +/*
> > > + * ENE KB3930 Embedded Controller Driver
> > > + *
> > > + * Copyright (C) 2020 Lubomir Rintel
> > > + */
> > > +
> > > +#include <linux/module.h>
> > > +#include <linux/i2c.h>
> > > +#include <linux/gpio/consumer.h>
> > > +#include <linux/delay.h>
> > > +#include <linux/reboot.h>
> > > +#include <linux/regmap.h>
> > > +#include <linux/mfd/core.h>
> > 
> > Alphabetical.
> > 
> > > +enum {
> > > +	EC_DATA_IN	= 0x00,
> > > +	EC_RAM_OUT	= 0x80,
> > > +	EC_RAM_IN	= 0x81,
> > > +};
> > 
> > Are these registers?
> 
> These are I2C registers that are multiplexing access to the EC RAM.
> Should I add a comment or make it clearer in some other way?

A comment sounds good.

> > > +enum {
> > > +	EC_MODEL_ID	= 0x30,
> > > +	EC_VERSION_MAJ	= 0x31,
> > > +	EC_VERSION_MIN	= 0x32,
> > > +};
> > 
> > As above?
> 
> These are the locations in EC RAM, multiplexed via EC_DATA_IN and
> EC_RAM_IN/OUT.

As above.

> > > +struct kb3930 {
> > > +	struct i2c_client *client;
> > > +	struct regmap *ec_ram;
> > 
> > This is usually called 'regmap'.
> 
> Yes. But the device has a set of registers directly on the I2C bus as
> well as another set of registers in the RAM access to which is
> multiplexed via a pair of I2C registers.
> 
> This regmap is for the latter register block which is the only one
> exposed currently. I believe it still makes sense to make it obvious
> this is not the I2C registers in case the driver is extended to expose
> those in future.

ram_regmap or similar.

> > > +	struct gpio_descs *off_gpios; 
> > > +};
> > > +
> > > +struct kb3930 *global_kb3930;
> > 
> > Globals are massively frowned upon.  Please move it.
> 
> This is necessary for the pm_power_off hook that takes no argument. All
> other MFD drivers that implement power off use a global:

Ah, it's one of those:

  static struct kb3920_power_off

>   ab8500-sysctrl.c: static struct device *sysctrl_dev;
>   axp20x.c:         static struct axp20x_dev *axp20x_pm_power_off;
>   dm355evm_msp.c:   static struct i2c_client *msp430;
>   max77620.c:       static struct max77620_chip *max77620_scratch;
>   max8907.c:        static struct max8907 *max8907_pm_off;
>   palmas.c:         static struct palmas *palmas_dev;
>   retu-mfd.c:       static struct retu_dev *retu_pm_power_off;
>   rk808.c:          static struct i2c_client *rk808_i2c_client;
>   rn5t618.c:        static struct rn5t618 *rn5t618_pm_power_off;
>   tps6586x.c:       static struct device *tps6586x_dev;
>   tps65910.c:       static struct i2c_client *tps65910_i2c_client;
>   tps80031.c:       static struct tps80031 *tps80031_power_off_dev;
>   twl-core.c:       static struct twl_private *twl_priv;

[...]

> > > +					   ariel_ec_cells,
> > > +					   ARRAY_SIZE(ariel_ec_cells),
> > > +					   NULL, 0, NULL);
> > > +		if (ret < 0)
> > > +			return ret;
> > > +	} else {
> > > +		dev_err(dev, "unknown board model: %02x\n", model_id);
> > > +		return -ENODEV;
> > 
> > If you reverse the logic here, you can put this in the if() and omit
> > the else.
> 
> It is intentionally structured this way.
> 
> Though the driver currently only supports the 'J' version of the EC
> firmware, other versions are possible, with different cells exposed via
> the EC RAM registers.

It's difficult to review based on whatifs.

I think it's worth doing it right for the current situation and adapt
it *if* things change in the future.

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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