[U-Boot] [PATCH 28/55] dm: pmic: max77686: Support all BUCK regulators

[Simon Glass]

Hi Przemyslaw,

On 10 July 2015 at 05:53, Przemyslaw Marczak <p.marczak at samsung.com> wrote:
>
> Hello Simon,
>
> On 07/03/2015 02:16 AM, Simon Glass wrote:
>>
>> Add support for all BUCK regulators, now that the correct register is
>> accessed for each.
>>
>> Signed-off-by: Simon Glass <sjg at chromium.org>
>>
>> ---
>>
>>   drivers/power/regulator/max77686.c | 10 +++-------
>>   1 file changed, 3 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/power/regulator/max77686.c b/drivers/power/regulator/max77686.c
>> index 21173fc..427b717 100644
>> --- a/drivers/power/regulator/max77686.c
>> +++ b/drivers/power/regulator/max77686.c
>> @@ -81,11 +81,7 @@ static int max77686_buck_volt2hex(int buck, int uV)
>>                 /* hex = (uV - 600000) / 12500; */
>>                 hex = (uV - MAX77686_BUCK_UV_LMIN) / MAX77686_BUCK_UV_LSTEP;
>>                 hex_max = MAX77686_BUCK234_VOLT_MAX_HEX;
>> -               /**
>> -                * Those use voltage scaller - temporary not implemented
>> -                * so return just 0
>> -                */
>> -               return -ENOSYS;
>> +               break;
>>         default:
>>                 /* hex = (uV - 750000) / 50000; */
>>                 hex = (uV - MAX77686_BUCK_UV_HMIN) / MAX77686_BUCK_UV_HSTEP;
>> @@ -379,11 +375,11 @@ static int max77686_buck_val(struct udevice *dev, int op, int *uV)
>>         case 2:
>>         case 3:
>>         case 4:
>> -               /* Those use voltage scallers - will support in the future */
>>                 mask = MAX77686_BUCK234_VOLT_MASK;
>> -               return -ENOSYS;
>> +               break;
>>         default:
>>                 mask = MAX77686_BUCK_VOLT_MASK;
>> +               break;
>>         }
>>
>>         ret = pmic_read(dev->parent, adr, &val, 1);
>>
>
> The bucks 2,3,4 can work in DVS mode, which allows select one of eight DVS regulators for each output. The default selection at power-on is DVS1 for each output, and it corresponds to the currently defined output register addresses.
>
> The selection can be done by six PMIC's GPIOs:
> - DVS1/2/3 - output selection: 0x0=DVS1...0x7=DVS8
> - SELB2/3/4 - mode switch: 'DVS' or 'no DVS'
>
> Reading or writing the default registers is proper only in case:
> - for the default PMIC's power-up setting - may conflict with bl1/bl2
> - when DVS1/2/3 GPIOs are set to LOW - DVS1 selected
> - SELB2/3/4 - are set to LOW - no DVS mode
>
> The documentation is poor, but if I good understand, the SELB is used as "latch" for the DVS selection.
>
> So the driver, could be unreliable for these outputs if it doesn't check the PMIC's GPIOs.
>
> It's quite confusing, since the PMIC, doesn't provide registers to check those GPIOs. It should be checked by the driver and can be delivered by device-tree.
>
> This is also confusing, since it depends on board design, because the PMIC's GPIOs can be connected to the SoCs GPIOs and also just pulled to POWER/GND signals.
>
> The documentation says, that those GPIOs should be set accordingly, and for example Odroid U3 has connected the SELB to VDD_IO(LDO3) power line, so actually this state can not be changed or can be changed by accident when changing the VDD_IO - which is HIGH at PMIC's power-up.
>
> The switching is impossible, since the VDD_IO line is shared with few other peripherals.
>
> In this case, maybe you should add config to allow use of the BUCK234 only for case in which DVS mode is disabled by board design (SELB2/3/4 set to LOW). This may also work, when the GPIOs of Exynos stays in the reset state.
>
> Then, using the default 'buck_out' registers: 0x14, 0x1e, 0x28 is reasonable.

I don't see anything in the binding. I have added a comment in the
driver to explain this limitation. However I haven't actually seen
hardware that makes use of it. Are you saying that Odroid U3 does use
it, or just that it has the lines connected up incorrectly?

>
> Did you tried measure the output voltage, after its change?

No I have not measured it, only verified that the code looks correct.
If you are able to do that I think it would be a good test.

>
> Regards,
> --
> Przemyslaw Marczak
> Samsung R&D Institute Poland
> Samsung Electronics
> p.marczak at samsung.com

Regards,
Simon