linux-kernel - Re: [PATCH] hwmon: (pmbus/lm25066) Default coefficients for low current limit

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Date:   Tue, 28 Nov 2017 10:39:10 -0800
From:   Rob Lippert <rlippert@...gle.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Robert Lippert <roblip@...il.com>, linux-hwmon@...r.kernel.org,
        jdelvare@...e.com, linux-kernel@...r.kernel.org,
        Xo Wang <xow@...gle.com>
Subject: Re: [PATCH] hwmon: (pmbus/lm25066) Default coefficients for low
 current limit

On Mon, Nov 27, 2017 at 8:26 PM, Guenter Roeck <linux@...ck-us.net> wrote:
> On 11/27/2017 04:28 PM, Robert Lippert wrote:
>>
>> There seems to be no way to detect the value of the CL/GAIN pin
>> from the device using PMBus.
>>
>> Low current mode seems to be recommended (from LM5066 datasheet) for
>> improved current reporting accuracy in a typical design.
>>
>> Assume the device is in low current mode unless the register override
>> bit is set and indicates high current limit mode.
>>
>> Signed-off-by: Robert Lippert <rlippert@...gle.com>
>
>
> Applied (silently fixed continuation line alignment).
>
> Looking at the most recent version of various datasheets for the chips
> supported
> by the driver, looks like TI changed the coefficients (again). Not the first
> time.
> Time to go through all chips and update coefficients. Might be worthwhile
> to do that at least for the chips(s) which are of interest for you.

This patch also needs commit "hwmon: (pmbus/lm25066) Swap low/high
current coefficients for LM5066(i)" to maintain the existing reporting
behavior for LM5066 devices atleast.
(as now it will be pulling from the _L values by default)

I spot checked the coeff values for lm25056 with the online datasheet
and they also seem to be swapped although it is a little hard to be
sure since the meaning of GAIN input seems to be opposite of CL input:
GAIN=0 is low current and GAIN=1 is high current.

-Rob

>
> Thanks,
> Guenter
>
>
>> ---
>>   drivers/hwmon/pmbus/lm25066.c | 19 +++++++++++++------
>>   1 file changed, 13 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/hwmon/pmbus/lm25066.c b/drivers/hwmon/pmbus/lm25066.c
>> index aa052f4449a9..f6ae7b4cf705 100644
>> --- a/drivers/hwmon/pmbus/lm25066.c
>> +++ b/drivers/hwmon/pmbus/lm25066.c
>> @@ -43,6 +43,7 @@ enum chips { lm25056, lm25063, lm25066, lm5064, lm5066,
>> lm5066i };
>>   #define LM25066_READ_AVG_IIN          0xde
>>   #define LM25066_READ_AVG_PIN          0xdf
>>   +#define LM25066_DEV_SETUP_CL_CONFIG  BIT(2)  /* Use pin or SMBus values
>> */
>>   #define LM25066_DEV_SETUP_CL          BIT(4)  /* Current limit */
>>     /* LM25056 only */
>> @@ -526,16 +527,22 @@ static int lm25066_probe(struct i2c_client *client,
>>         info->R[PSC_VOLTAGE_OUT] = coeff[PSC_VOLTAGE_OUT].R;
>>         info->R[PSC_CURRENT_IN] = coeff[PSC_CURRENT_IN].R;
>>         info->R[PSC_POWER] = coeff[PSC_POWER].R;
>> -       if (config & LM25066_DEV_SETUP_CL) {
>> -               info->m[PSC_CURRENT_IN] = coeff[PSC_CURRENT_IN_L].m;
>> -               info->b[PSC_CURRENT_IN] = coeff[PSC_CURRENT_IN_L].b;
>> -               info->m[PSC_POWER] = coeff[PSC_POWER_L].m;
>> -               info->b[PSC_POWER] = coeff[PSC_POWER_L].b;
>> -       } else {
>> +
>> +       /*
>> +        * Assume chip is in low current limit/gain mode by default unless
>> +        * the register override is asserted AND indicates high limit
>> mode.
>> +        */
>> +       if ((config & LM25066_DEV_SETUP_CL_CONFIG) &&
>> +               (config & LM25066_DEV_SETUP_CL)) {
>>                 info->m[PSC_CURRENT_IN] = coeff[PSC_CURRENT_IN].m;
>>                 info->b[PSC_CURRENT_IN] = coeff[PSC_CURRENT_IN].b;
>>                 info->m[PSC_POWER] = coeff[PSC_POWER].m;
>>                 info->b[PSC_POWER] = coeff[PSC_POWER].b;
>> +       } else {
>> +               info->m[PSC_CURRENT_IN] = coeff[PSC_CURRENT_IN_L].m;
>> +               info->b[PSC_CURRENT_IN] = coeff[PSC_CURRENT_IN_L].b;
>> +               info->m[PSC_POWER] = coeff[PSC_POWER_L].m;
>> +               info->b[PSC_POWER] = coeff[PSC_POWER_L].b;
>>         }
>>         return pmbus_do_probe(client, id, info);
>>
>