On 12/21/20 10:32 AM, Eddie James wrote:
> On Mon, 2020-12-21 at 08:54 -0800, Guenter Roeck wrote:
>> On 12/21/20 8:30 AM, Eddie James wrote:
>>> Some PMBus chips don't respond with valid data when reading the
>>> CAPABILITY register. For instance the register may report that the
>>> chip supports PEC when in reality it does not. For such chips, PEC
>>> must not be enabled while probing the chip, so add a flag so that
>>> device drivers can force PEC off.
>>>
>>
>> I think the flag should indicate that the capability register
>> shall not be read/used. That the capability register is currently
>> only used to check for PEC is secondary. We might,for example,
>> start using it to check for alert support or to check the numeric
>> format.
>
> OK, that makes sense. I'll rename the flag in v2, how does
> PMBUS_NO_CAPABILITY sound?
>
sgtm
Thanks,
Guenter
> Thanks for the quick reply,
> Eddie
>
>>
>> Thanks,
>> Guenter
>>
>>> Signed-off-by: Eddie James <eajames@xxxxxxxxxxxxx>
>>> ---
>>> drivers/hwmon/pmbus/pmbus_core.c | 8 +++++---
>>> include/linux/pmbus.h | 10 ++++++++++
>>> 2 files changed, 15 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/hwmon/pmbus/pmbus_core.c
>>> b/drivers/hwmon/pmbus/pmbus_core.c
>>> index 192442b3b7a2..3de1657dde35 100644
>>> --- a/drivers/hwmon/pmbus/pmbus_core.c
>>> +++ b/drivers/hwmon/pmbus/pmbus_core.c
>>> @@ -2204,9 +2204,11 @@ static int pmbus_init_common(struct
>>> i2c_client *client, struct pmbus_data *data,
>>> }
>>>
>>> /* Enable PEC if the controller supports it */
>>> - ret = i2c_smbus_read_byte_data(client, PMBUS_CAPABILITY);
>>> - if (ret >= 0 && (ret & PB_CAPABILITY_ERROR_CHECK))
>>> - client->flags |= I2C_CLIENT_PEC;
>>> + if (!(data->flags & PMBUS_NO_PEC)) {
>>> + ret = i2c_smbus_read_byte_data(client,
>>> PMBUS_CAPABILITY);
>>> + if (ret >= 0 && (ret & PB_CAPABILITY_ERROR_CHECK))
>>> + client->flags |= I2C_CLIENT_PEC;
>>> + }
>>>
>>> /*
>>> * Check if the chip is write protected. If it is, we can not
>>> clear
>>> diff --git a/include/linux/pmbus.h b/include/linux/pmbus.h
>>> index 1ea5bae708a1..9bdc8a581b03 100644
>>> --- a/include/linux/pmbus.h
>>> +++ b/include/linux/pmbus.h
>>> @@ -34,6 +34,16 @@
>>> */
>>> #define PMBUS_WRITE_PROTECTED BIT(1)
>>>
>>> +/*
>>> + * PMBUS_NO_PEC
>>> + *
>>> + * Some PMBus chips don't respond with valid data when reading the
>>> CAPABILITY
>>> + * register. In this case, the register may report that the chip
>>> supports PEC
>>> + * with bit 7 (PB_CAPABILITY_ERROR_CHECK) when in reality it's not
>>> supported.
>>> + * For such chips, PEC must not be enabled before probing the
>>> chip.
>>> + */
>>> +#define PMBUS_NO_PEC BIT(2)
>>> +
>>> struct pmbus_platform_data {
>>> u32 flags; /* Device specific flags */
>>>
>>>
>
