lkml.org 
[lkml]   [2017]   [Nov]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] hwmon: (pmbus/lm25066) Default coefficients for low current limit
From
Date
On 11/28/2017 10:39 AM, Rob Lippert wrote:
> On Mon, Nov 27, 2017 at 8:26 PM, Guenter Roeck <linux@roeck-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@google.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;
>>> }

After looking into it more closely, turns out this is wrong.

The _L defines were supposed to be used if bit 4 is set, not if it is unset.
It wasn't supposed to mean "low" but "CL/GAIN=1" (ok, looking at it with 20/20
hindsight, that seems to be odd, but it is consistent with the code).

So the code should be something like

if ((config & LM25066_DEV_SETUP_CL_CONFIG) &&
(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 {
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;
}

Only that by itself is insufficient because not all chips support
bit 2 (at least lm25056 doesn't). We can work around that with
something like

if (data->id == lm25056)
config |= LM25066_DEV_SETUP_CL_CONFIG;

Can you do that ?

[ LM25063 doesn't have the bit either, but it looks like TI acquired
National before LM25063 shipped, and the chip was never actually
released. Dropping that will be a separate patch. ]

Thanks,
Guenter

\
 
 \ /
  Last update: 2017-11-29 03:26    [W:0.074 / U:0.056 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site