linux-kernel - Re: [PATCH] regulator: pwm: Fix regulator ramp delay for continuous mode

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Date:	Wed, 6 Jul 2016 11:31:45 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:	Mark Brown <broonie@...nel.org>, Lee Jones <lee.jones@...aro.org>,
	Brian Norris <briannorris@...omium.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Liam Girdwood <lgirdwood@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] regulator: pwm: Fix regulator ramp delay for continuous mode

Boris,

On Wed, Jul 6, 2016 at 5:27 AM, Boris Brezillon
<boris.brezillon@...e-electrons.com> wrote:
> On Mon, 27 Jun 2016 21:53:11 -0700
> Douglas Anderson <dianders@...omium.org> wrote:
>
>> The original commit adding support for continuous voltage mode didn't
>> handle the regulator ramp delay properly.  It treated the delay as a
>> fixed delay in uS despite the property being defined as uV / uS.  Let's
>> adjust it.  Luckily there appear to be no users of this ramp delay for
>> PWM regulators (as per grepping through device trees in linuxnext).
>>
>> Note also that the upper bound of usleep_range probably shouldn't be a
>> full 1 ms longer than the lower bound since I've seen plenty of hardware
>> with a ramp rate of ~5000 uS / uV and for small jumps the total delays
>> are in the tens of uS.  1000 is way too much.  We'll try to be dynamic
>> and use 10%
>
> I realize I may have introduced another bug when adding the
> ->enable()/disable() methods: we are only waiting for the ramp up delay
> when changing the voltage, but it should probably be applied when
> enabling the PWM, and conditionally applied when changing the voltage
> only if the PWM is enabled.

I'll certainly let Mark comment here, but:

* For enabling the PWM, I think you want want "regulator-enable-ramp-delay".

* Right, we probably shouldn't be delaying if the regulator is off.
I'll add that to my patch.

-Doug