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

["Jonathan Neuschäfer" <j.neuschaefer@gmx.net>]

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On Fri, Sep 25, 2020 at 12:29:45PM +0300, Andy Shevchenko wrote:
> 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)

I think it was a leftover from v1 before I used regmap for general
access to the registers. Will fix the ordering.

> > +#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.

Good idea.

> > +       };
> > +       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.

Ok.

> 
> > +               }
> > +       };
> > +
> > +       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.

I copied the dev_alert from drivers/mfd/rn5t618.c.

Upon reconsideration, I'm not sure what the correct log level would be,
but _warn seems enough, or maybe _err is better

> > +       /*
> > +        * 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 ?

Unknown, because I don't have the EC firmware for analysis. The vendor
kernel sends 0xff00 and gets an error.

Sending 0xffff doesn't help.

> > +        */
> > +       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.

Okay, will do.

> 
> > +       };
> > +       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;
> > +}
> 
> ...

An error in the i2c transfer here is an abnormal situation that should
in my opinion be logged, but I don't see what else the code can do here
to handle the error.

> 
> > +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.

Right. I suppose printing incompatible versions is still useful, so how
about something like the following?


       /* Bail out if we encounter an unknown firmware version */
       switch (version) {
       case 0xd726: /* found in Kobo Aura */
	       dev_info(ec->dev,
			"Netronix embedded controller version %04x detected.\n",
			version);
               break;
       default:
	       dev_err(ec->dev,
			"Netronix embedded controller version %04x is not supported.\n",
			version);
               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 being already set is not a situation that should
happen (and would indicate a bug in this driver, AFAICT), but I guess
the log message could be better in that case...

> > +               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.

Okay, I'll change it to dev_err.

> 
> 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?

The EC doesn't always need to provide poweroff/restart functionality,
and AFAIK, in some systems it doesn't. In those systems, ntxec_remove
would run with poweroff_restart_client == NULL.

In theory, there might also be two of it in the same system, of which
only one controls system poweroff/restart, but I'm not sure if that is
actually the case on any existing board design.

> > +               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.

I'll add them.

> > +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.

I didn't think of it, but it's a good idea. Will do.


Thanks,
Jonathan Neuschäfer

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