Re: [PATCH v2 3/6] hwmon: (pmbus/pim4328) Add support for reading direct format coefficients

From: Erik Rosen
Date: Sun May 23 2021 - 13:53:07 EST

On Sat, May 22, 2021 at 3:41 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>
> On 5/22/21 3:55 AM, Erik Rosen wrote:
> > Add support for reading and decoding direct format coefficients to
> > the PMBus core driver. If the new flag PMBUS_USE_COEFFICIENTS_CMD
> > is set, the driver will use the COEFFICIENTS register together with
> > the information in the pmbus_sensor_attr structs to initialize
> > relevant coefficients for the direct mode format.
> >
> > Signed-off-by: Erik Rosen <erik.rosen@xxxxxxxxxxxxx>
> > ---
> > drivers/hwmon/pmbus/pmbus_core.c | 93 ++++++++++++++++++++++++++++++++
> > include/linux/pmbus.h | 8 +++
> > 2 files changed, 101 insertions(+)
> >
> > diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> > index 460cbfd716e4..03c169bf5633 100644
> > --- a/drivers/hwmon/pmbus/pmbus_core.c
> > +++ b/drivers/hwmon/pmbus/pmbus_core.c
> > @@ -2177,6 +2177,38 @@ static int pmbus_find_attributes(struct i2c_client *client,
> > return ret;
> > }
> >
> > +static int pmbus_init_coefficients(struct i2c_client *client,
> > + struct pmbus_data *data, int page,
>
> This seems wrong. Coefficients are not maintained per page but per class,
> and (re-)reading them for each supported page doesn't really add value or
> even make sense.
>
> > + enum pmbus_sensor_classes sensor_class,
> > + const struct pmbus_sensor_attr *attrs,
> > + int nattrs)
> > +{
> > + int i, status;
> > +
> > + for (i = 0; i < nattrs; i++) {
> > + if (attrs->class == sensor_class &&
> > + (attrs->func & data->info->func[page])) {
> > + status = pmbus_read_coefficients(client,
> > + (struct pmbus_driver_info *)data->info,
> > + sensor_class,
> > + attrs->reg);
> > + if (status < 0) {
> > + dev_err(&client->dev,
> > + "Failed to read coefficients for register: %x\n",
> > + attrs->reg);
> > + return status;
> > + }
> > + return 0;
> > + }
> > + attrs++;
> > + }
> > +
> > + dev_err(&client->dev, "No coefficients found for register: %x\n",
> > + attrs->reg);
> > +
>
> attrs points beyond the array size here, so attrs->reg does not point
> to a valid array element. The problem would also not be the register
> this happens to point to, but the class (ie the chip does not support
> a sensor of the requested class).
>
> Not sure if this should trigger a message or error in the first place.
> It won't matter since the chip will never need those coefficients.
> If anything, this would be a misconfiguration (the driver should
> not set direct format for this sensor class), and the return value
> should be -EINVAL.
>
> Either case, I wonder if this can be handled with less complex code,
> ie without having to check data->info->func[] for all pages. How
> about just walking through attrs and try all class matches until
> one is found that works (ie not return on error but keep trying) ?

Ok, I'll send a new version based on your comments.
I'm not entirely comfortable with just silently ignoring any failure to
retrieve the coefficients for a sensor class. I mean it could be due to any
reason; a bus error for instance. I'll return a -EINVAL for now if you don't
disagree.

/Erik

>
> > + return -ENODEV;
> > +}
> > +
> > /*
> > * Identify chip parameters.
> > * This function is called for all chips.
> > @@ -2185,6 +2217,7 @@ static int pmbus_identify_common(struct i2c_client *client,
> > struct pmbus_data *data, int page)
> > {
> > int vout_mode = -1;
> > + int ret;
> >
> > if (pmbus_check_byte_register(client, page, PMBUS_VOUT_MODE))
> > vout_mode = _pmbus_read_byte_data(client, page,
> > @@ -2214,6 +2247,66 @@ static int pmbus_identify_common(struct i2c_client *client,
> > }
> > }
> >
> > + if (data->flags & PMBUS_USE_COEFFICIENTS_CMD) {
>
> I think there should be a separate function to handle that,
> to be called only once, not once per page.
>
> > + if (!i2c_check_functionality(client->adapter,
> > + I2C_FUNC_SMBUS_BLOCK_PROC_CALL))
> > + return -ENODEV;
> > +
> > + if (data->info->format[PSC_VOLTAGE_IN] == direct) {
> > + ret = pmbus_init_coefficients(client, data, page,
> > + PSC_VOLTAGE_IN,
> > + voltage_attributes,
> > + ARRAY_SIZE(voltage_attributes));
> > + if (ret)
> > + return ret;
> > + }
>
> It might be useful to have a little structure with {class, attribute list pointer,
> attribute list size} and walk through that in a loop instead of repeating essentially
> the same code multiple times.
>
> > +
> > + if (data->info->format[PSC_VOLTAGE_OUT] == direct) {
> > + ret = pmbus_init_coefficients(client, data, page,
> > + PSC_VOLTAGE_OUT,
> > + voltage_attributes,
> > + ARRAY_SIZE(voltage_attributes));
> > + if (ret)
> > + return ret;
> > + }
> > +
> > + if (data->info->format[PSC_CURRENT_IN] == direct) {
> > + ret = pmbus_init_coefficients(client, data, page,
> > + PSC_CURRENT_IN,
> > + current_attributes,
> > + ARRAY_SIZE(current_attributes));
> > + if (ret)
> > + return ret;
> > + }
> > +
> > + if (data->info->format[PSC_CURRENT_OUT] == direct) {
> > + ret = pmbus_init_coefficients(client, data, page,
> > + PSC_CURRENT_OUT,
> > + current_attributes,
> > + ARRAY_SIZE(current_attributes));
> > + if (ret)
> > + return ret;
> > + }
> > +
> > + if (data->info->format[PSC_POWER] == direct) {
> > + ret = pmbus_init_coefficients(client, data, page,
> > + PSC_POWER,
> > + power_attributes,
> > + ARRAY_SIZE(power_attributes));
> > + if (ret)
> > + return ret;
> > + }
> > +
> > + if (data->info->format[PSC_TEMPERATURE] == direct) {
> > + ret = pmbus_init_coefficients(client, data, page,
> > + PSC_TEMPERATURE,
> > + temp_attributes,
> > + ARRAY_SIZE(temp_attributes));
> > + if (ret)
> > + return ret;
> > + }
> > + }
> > +
> > pmbus_clear_fault_page(client, page);
> > return 0;
> > }
> > diff --git a/include/linux/pmbus.h b/include/linux/pmbus.h
> > index f720470b1bab..7fdc282dab5a 100644
> > --- a/include/linux/pmbus.h
> > +++ b/include/linux/pmbus.h
> > @@ -52,6 +52,14 @@
> > */
> > #define PMBUS_NO_WRITE_PROTECT BIT(4)
> >
> > +/*
> > + * PMBUS_USE_COEFFICIENTS_CMD
> > + *
> > + * When this flag is set the PMBus core driver will use the COEFFICIENTS
> > + * register to initialize the coefficients for the direct mode format.
> > + */
> > +#define PMBUS_USE_COEFFICIENTS_CMD BIT(5)
> > +
> > struct pmbus_platform_data {
> > u32 flags; /* Device specific flags */
> >
> >
>