Re: [PATCH v3 2/2] regulator: rk808: add dvs support

[Chris Zhong <zyw@rock-chips.com>]

On 12/31/2014 01:04 AM, Mark Brown wrote:
> On Tue, Dec 30, 2014 at 11:07:14AM +0800, Chris Zhong wrote:
>> On 12/30/2014 01:25 AM, Mark Brown wrote:
>>> So, this seems a bit odd.  What we appear to be doing here is
>>> alternating between the two different voltage setting registers which is
>>> all well and good but makes me wonder why we're bothering - it's a bit
>>> more work than just sticking with one.  We do get...
>> you mean check the old_selector and selector? I think
>> _regulator_do_set_voltage have done it.
> No, I mean that we may as well just always write to the same register
> and save a bunch of code.
No, when we pull down DVSn pin, the voltage value is from 
RK808_BUCK1_ON_VSEL_REG,
and when we pull up DVSn pin, the voltage value if from 
RK808_BUCK1_ON_VSEL_REG+2.
We want to this dvs function for a better voltage wave, avoid overshoot, 
if someone do not
need this function, they could remove the setting of DVSn pin in dts 
file, and at that time,
rk808_regulator will use a same register for setting voltage.


>>> ...this but unless the voltage typically ramps much faster than spec
>>> it's never clear to me that we're actually winning by polling the pin
>>> instead of just dead reckoning the time, it's more work for the CPU to
>>> poll the GPIO than to sleep after all.
>> Actually, it's slower than spec, so I think getting this dvsok pin state
>> is safer than delay.
> Well, that suggests that the spec is wrong which ought to be fixed
> anyway oughtn't it?  Or are you saying that the delay is inconsistent as
> well as slower than advertised?
the spec said 2/4/6/10 mv/us, but the ramp will change depending on the 
load.
So I think the dvsok pin is more accurate, since it It will soon change, 
once the
regulator is completed. the delay is a fixed time. it is faster than 
dvsok pin.