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

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

On 12/30/2014 01:25 AM, Mark Brown wrote:
> On Mon, Dec 15, 2014 at 11:07:58AM +0800, Chris Zhong wrote:
>
>> +	sel <<= ffs(rdev->desc->vsel_mask) - 1;
>> +	sel |= old_sel & ~rdev->desc->vsel_mask;
>> +
>> +	ret = regmap_write(rdev->regmap, reg, sel);
>> +	if (ret)
>> +		return ret;
>> +
>> +	gpiod_set_value(gpio, !gpio_level);
> 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.
>
>> +	/*
>> +	 * dvsok pin would be pull down when dvs1/2 pin changed, and
>> +	 * it would be pull up once the voltage regulate complete.
>> +	 * No need to wait dvsok signal when voltage falling.
>> +	 */
> ...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.
>
> One thing we can do with hardware like this is to program in a voltage
> we're likely to want to switch to quickly and then use the GPIO to get
> there.  That can be a bit hard to arrange with the regulator API as it
> currently stands since we don't exactly have an interface for it.
>
> We can just check to see what the two values are current set to before
> switching and skip the register write if it's the same (making things
> faster since we're typically avoiding an I2C or SPI transaction by doing
> that) but that's a bit meh.  We can also try to do things like keep the
> top voltage from the voltage ranges we're being given programmed which
> for DVS typically ends up doing a reasonable job since governors often
> like to jump straight to top speed when things get busy so that's one of
> the common cases where we most want to change voltages as quickly as
> possible.