[PATCH linux dev-5.8] hwmon: Ampere Computing ALTRA SMPMPRO sensor driver

[Joel Stanley]

On Thu, 1 Oct 2020 at 12:32, Patrick Williams <patrick at stwcx.xyz> wrote:
>
> On Wed, Sep 30, 2020 at 05:26:57PM -0500, Lancelot wrote:
> > From: Lancelot Kao <lancelot.kao at fii-usa.com>
> >
> > Add SMPMPro-hwmon driver to monitor Ampere CPU/Memory/VR via an
> > i2c interface of the CPU's smpmpro management device.
> >
> > Signed-off-by: Xiaopeng XP Chen <xiao-peng.chen at fii-na.com>
> > Signed-off-by: Lancelot Kao <lancelot.kao at fii-usa.com>
>
> Nice work at adding this driver.
>
> It does look like you've missed CC'ing upstream though.  Was this
> intentional?  (linux-hwmon at vger.kernel.org)

As Patrick mentioned, let's review this on the upstream list.

Cheers,

Joel

>
> > +/* Capability Registers  */
> > +#define TEMP_SENSOR_SUPPORT_REG      0x05
> > +#define PWR_SENSOR_SUPPORT_REG       0x06
> > +#define VOLT_SENSOR_SUPPORT_REG      0x07
> > +#define OTHER_CAP_REG                    0x08
> > +#define CORE_CLUSTER_CNT_REG 0x0B
> > +#define SYS_CACHE_PCIE_CNT_REG       0x0C
> > +#define SOCKET_INFO_REG              0x0D
>
> There seems to be some sporatic indentation throughout all the #defines
> in this file, where it appears you attempted to align the values.  Make
> sure you have tabs set to 8-step spacing for kernel code.
>
> > +static void smpmpro_init_device(struct i2c_client *client,
> > +                             struct smpmpro_data *data)
> > +{
> > +     u16 ret;
> > +
> > +     ret = i2c_smbus_read_word_swapped(client, TEMP_SENSOR_SUPPORT_REG);
> > +     if (ret < 0)
> > +             return;
> > +     data->temp_support_regs = ret;
>
> i2c_smbus_read_word_swapped returns a s32 even though you're looking for
> a u16.  By setting `ret` to u16 you've caused two problems:
>
>     * You are immediately truncating -ERRNO values into a u16 so that
>       you are unable to differentiate values like 0xFFFFFFFF as a
>       register value and -1 as an errno.
>
>     * The if condition here can never be true, so you're never catching
>       error conditions.  (An u16 can never be negative, so ret < 0 can
>       never be true.)
>
> This issue occurs throughout the driver.
>
> > +static int smpmpro_read_temp(struct device *dev, u32 attr, int channel,
> > +                          long *val)
> > +{
> > +     struct smpmpro_data *data = dev_get_drvdata(dev);
> > +     struct i2c_client *client = data->client;
> > +     int ret;
>
> You might want a sized int on this one?  Repeated in most other
> functions.
>
> > +static int smpmpro_read_power(struct device *dev, u32 attr, int channel,
> > +                          long *val)
> > +{
> > +     struct smpmpro_data *data = dev_get_drvdata(dev);
> > +     struct i2c_client *client = data->client;
> > +     int ret, ret_mw;
> > +     int ret2 = 0, ret2_mw = 0;
>
> Any reason to not initialize ret/ret_mw?  By it being different from
> ret2/ret2_mw it makes me question "is this ok?", which spends more time
> in review.
>
> > +static int smpmpro_i2c_probe(struct i2c_client *client,
> > +                       const struct i2c_device_id *id)
> ...
> > +     /* Initialize the Altra SMPMPro chip */
> > +     smpmpro_init_device(client, data);
>
> I didn't see anything in the smpmpro_init_device function, but is there
> anything you can or should do to ensure this device really is an
> SMPMPro rather than exclusively relying on the device tree compatible?
>
> > +static struct i2c_driver smpmpro_driver = {
> > +     .class          = I2C_CLASS_HWMON,
> > +     .probe          = smpmpro_i2c_probe,
> > +     .driver = {
> > +             .name   = "smpmpro",
> > +     },
> > +     .id_table       = smpmpro_i2c_id,
> > +};
> > +
> > +module_i2c_driver(smpmpro_driver);
>
> Are you missing the .of_match_table inside .driver?  Is that necessary
> or useful for your use?  I'm not sure if you can have device tree
> entries that automatically instantiate the hwmon driver otherwise.
>
> --
> Patrick Williams