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

[Przemyslaw Marczak]

Hello Simon,

On 07/30/2015 04:05 AM, Simon Glass wrote:
> 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?
>

Right, the binding for those GPIOs don't exists, since change of those 
registers values was not supported by the driver before.

I looked into the bl2 code from the Hardkernel's U-Boot (we are using 
it's signed bl2 binary for U3). There is a code for smdk4212/smdk4412, 
which is reused for Odroid U3 and the bl2 MAX77686 driver configures the 
DVS/SELB gpios. Unfortunately the GPIO is invalid, probably it is valid 
for smdk.

Code:
https://github.com/hardkernel/u-boot/blob/odroid-v2010.12/board/samsung/smdk4212/pmic.c#L707


In the hardkernel's code we can also see the MAX77686 driver for 
smdk5250, which also sets the DVS/SELB by GPD/GPX pins in a proper way.

Code:
https://github.com/hardkernel/u-boot/blob/odroid-v2010.12/board/samsung/smdk5250/pmic.c#L546


>>
>> 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.
>

At present I can't measure it, but it should be verified in the future.
But if you can notice a stability change after setting those registers, 
then we can assume, that it works.

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

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