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

[Przemyslaw Marczak <p.marczak@samsung.com>]

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@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.

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

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