Re: [PATCH v3 3/7] mfd: Add base driver for Netronix embedded controller

[Andy Shevchenko <andy.shevchenko@gmail.com>]

On Thu, Sep 24, 2020 at 10:26 PM Jonathan Neuschäfer
<j.neuschaefer@gmx.net> wrote:
>
> The Netronix embedded controller is a microcontroller found in some
> e-book readers designed by the ODM Netronix, Inc. It contains RTC,
> battery monitoring, system power management, and PWM functionality.
>
> This driver implements register access and version detection.
>
> Third-party hardware documentation is available at:
>
>   https://github.com/neuschaefer/linux/wiki/Netronix-MSP430-embedded-controller
>
> The EC supports interrupts, but the driver doesn't make use of them so
> far.

...

> +#include <asm/unaligned.h>

This usually goes after linux/*.h
(and actually not visible how it's being used, but see below first)

> +#include <linux/delay.h>
> +#include <linux/errno.h>
> +#include <linux/i2c.h>
> +#include <linux/mfd/core.h>
> +#include <linux/mfd/ntxec.h>
> +#include <linux/module.h>
> +#include <linux/pm.h>
> +#include <linux/reboot.h>
> +#include <linux/regmap.h>
> +#include <linux/types.h>

...

> +static void ntxec_poweroff(void)
> +{
> +       int res;
> +       u8 buf[] = {
> +               NTXEC_REG_POWEROFF,

> +               (NTXEC_POWEROFF_VALUE >> 8) & 0xff,
> +               NTXEC_POWEROFF_VALUE & 0xff,

'& 0xff' parts are redundant. *u8 implies that. Fix in all cases.
Also I would rather see something like

  buf[0] = _POWEROFF;
  put_unaligned_be16(_VALUE, &buf[1]);

to explicitly show the endianess of the register values.

> +       };
> +       struct i2c_msg msgs[] = {
> +               {
> +                       .addr = poweroff_restart_client->addr,
> +                       .flags = 0,
> +                       .len = sizeof(buf),

> +                       .buf = buf

It's slightly better to keep trailing commas in cases like this.

> +               }
> +       };
> +
> +       res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
> +       if (res < 0)

> +               dev_alert(&poweroff_restart_client->dev,
> +                         "Failed to power off (err = %d)\n", res);

alert? This needs to be explained.

> +       /*
> +        * The time from the register write until the host CPU is powered off
> +        * has been observed to be about 2.5 to 3 seconds. Sleep long enough to
> +        * safely avoid returning from the poweroff handler.
> +        */
> +       msleep(5000);
> +}
> +
> +static int ntxec_restart(struct notifier_block *nb,
> +                        unsigned long action, void *data)
> +{
> +       int res;
> +       /*
> +        * NOTE: The lower half of the reset value is not sent, because sending
> +        * it causes an error

Why? Any root cause? Perhaps you need to send 0xffff ?

> +        */
> +       u8 buf[] = {
> +               NTXEC_REG_RESET,

> +               (NTXEC_RESET_VALUE >> 8) & 0xff,

Here you may still use put_unaligned_be16() but move the comment to be
before len hardcoded to sizeof(buf) - 1.

> +       };
> +       struct i2c_msg msgs[] = {
> +               {
> +                       .addr = poweroff_restart_client->addr,
> +                       .flags = 0,
> +                       .len = sizeof(buf),
> +                       .buf = buf
> +               }
> +       };
> +
> +       res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
> +       if (res < 0)
> +               dev_alert(&poweroff_restart_client->dev,
> +                         "Failed to restart (err = %d)\n", res);
> +
> +       return NOTIFY_DONE;
> +}

...

> +static int ntxec_probe(struct i2c_client *client)
> +{
> +       struct ntxec *ec;
> +       unsigned int version;
> +       int res;
> +
> +       ec = devm_kmalloc(&client->dev, sizeof(*ec), GFP_KERNEL);
> +       if (!ec)
> +               return -ENOMEM;
> +
> +       ec->dev = &client->dev;
> +
> +       ec->regmap = devm_regmap_init_i2c(client, &regmap_config);
> +       if (IS_ERR(ec->regmap)) {
> +               dev_err(ec->dev, "Failed to set up regmap for device\n");
> +               return res;
> +       }
> +
> +       /* Determine the firmware version */
> +       res = regmap_read(ec->regmap, NTXEC_REG_VERSION, &version);
> +       if (res < 0) {
> +               dev_err(ec->dev, "Failed to read firmware version number\n");
> +               return res;
> +       }

> +       dev_info(ec->dev,
> +                "Netronix embedded controller version %04x detected.\n",
> +                version);

This info level may confuse users if followed by an error path.

> +       /* Bail out if we encounter an unknown firmware version */
> +       switch (version) {
> +       case 0xd726: /* found in Kobo Aura */
> +               break;
> +       default:
> +               return -ENODEV;
> +       }
> +
> +       if (of_device_is_system_power_controller(ec->dev->of_node)) {
> +               /*
> +                * Set the 'powerkeep' bit. This is necessary on some boards
> +                * in order to keep the system running.
> +                */
> +               res = regmap_write(ec->regmap, NTXEC_REG_POWERKEEP,
> +                                  NTXEC_POWERKEEP_VALUE);
> +               if (res < 0)
> +                       return res;

> +               WARN_ON(poweroff_restart_client);

WARN_ON? All these alerts, WARNs, BUGs must be explained. Screaming to
the user is not good if it wasn't justified.

> +               poweroff_restart_client = client;
> +               if (pm_power_off)
> +                       dev_err(ec->dev, "pm_power_off already assigned\n");
> +               else
> +                       pm_power_off = ntxec_poweroff;
> +
> +               res = register_restart_handler(&ntxec_restart_handler);
> +               if (res)
> +                       dev_err(ec->dev,
> +                               "Failed to register restart handler: %d\n", res);
> +       }
> +
> +       i2c_set_clientdata(client, ec);
> +
> +       res = devm_mfd_add_devices(ec->dev, PLATFORM_DEVID_NONE, ntxec_subdevices,
> +                                  ARRAY_SIZE(ntxec_subdevices), NULL, 0, NULL);
> +       if (res)

> +               dev_warn(ec->dev, "Failed to add subdevices: %d\n", res);

'warn' is inconsistent with 'return err'. Either do not return an
error, or mark a message as an error one.

And above with the restart handler has the same issue.

> +       return res;
> +}
> +
> +static int ntxec_remove(struct i2c_client *client)
> +{

> +       if (client == poweroff_restart_client) {

When it's not the case?

> +               poweroff_restart_client = NULL;
> +               pm_power_off = NULL;
> +               unregister_restart_handler(&ntxec_restart_handler);
> +       }
> +
> +       return 0;
> +}

...

> +#include <linux/types.h>
> +

Missed

struct device;
struct regmap;

here.

> +struct ntxec {
> +       struct device *dev;
> +       struct regmap *regmap;
> +};

> +/*
> + * Some registers, such as the battery status register (0x41), are in
> + * big-endian, but others only have eight significant bits, which are in the
> + * first byte transmitted over I2C (the MSB of the big-endian value).
> + * This convenience function converts an 8-bit value to 16-bit for use in the
> + * second kind of register.
> + */
> +static inline u16 ntxec_reg8(u8 value)
> +{
> +       return value << 8;
> +}

I'm wondering why __be16 is not used as returned type.

-- 
With Best Regards,
Andy Shevchenko