On Thu, Jul 28, 2011 at 12:23 PM, Philip Rakity <prakity@xxxxxxxxxxx> wrote:
>
> On Jul 27, 2011, at 7:44 PM, zhangfei gao wrote:
>
>>>> +
>>>> +static struct fixed_voltage_config sdio_power = {
>>>> + .supply_name = "vmmc",
>>>> + .microvolts = 3000000,
>>>> + .gpio = mfp_to_gpio(MFP_PIN_GPIO57),
>>>> + .enable_high = 1,
>>>> + .enabled_at_boot = 0,
>>>> + .init_data = &sdio_power_data,
>>>> +};
>>>> +
>>>
>>> ldo7 is the power source. The 8787 is the consumer and the code should reflect this.
>>> GPIO57 is an on/off switch to the 8787.
>>>
>>>
>> Instead of LDO7, 8787 is powered with V_SD2, V_BATT, and VLDO12 on brownstone.
>> Use PDn to control 8787 power is recommended method.
>> 1. Some LDO is shared and can not be cut down.
>> 2. Control LDO is much slower, some time is needed for voltage to
>> decay, and the time is not accurate to control.
>> 3. With LDO powered, 8787 is under control and 8787 could put itself
>> to the lowest state.
>
>
> LDO is dedicated to 8787 and can be left on. The power picture is ldo (as regulator)
> and 8787 as consumer. Code does not show this relationship. The 8787 in deep sleep
> draws very little power but since even this small power usage is a concern the disabling
> the ldo can reduce power further.
In fact, disable ldo may consume more power than put 8787 in low power
mode, since leakage from pin, which can not be controlled by 8787 any
more if ldo is disabled.
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