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Date: Sun, 23 May 2021 12:47:46 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Erik Rosen <erik.rosen@...ormote.com>
Cc: Jean Delvare <jdelvare@...e.com>, Jonathan Corbet <corbet@....net>,
linux-hwmon@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/6] hwmon: (pmbus/pim4328) Add support for reading
direct format coefficients
On 5/23/21 10:52 AM, Erik Rosen wrote:
> On Sat, May 22, 2021 at 3:41 PM Guenter Roeck <linux@...ck-us.net> 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@...ormote.com>
>>> ---
>>> 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.
>
Ok. After all, it does suggest a misconfiguration.
Thanks,
Guenter
> /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 */
>>>
>>>
>>
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