Re: [linux-sunxi] Re: [PATCH 52/54] arm64: dts: allwinner: Remove regulator-ramp-delay

Chen-Yu Tsai
2021-08-06T12:08:10Z

On Fri, Aug 6, 2021 at 7:49 PM Icenowy Zheng <icenowy@aosc.io> wrote:
>
> 在 2021-07-22星期四的 10:16 +0200，Maxime Ripard写道：
> > On Thu, Jul 22, 2021 at 12:55:53AM -0500, Samuel Holland wrote:
> > > On 7/21/21 9:04 AM, Maxime Ripard wrote:
> > > > The regulator-ramp-delay property isn't documented in the binding
> > > > for
> > > > the AXP806, and it's ignored by the driver. Remove those
> > > > properties.
> > >
> > > This is a generic regulator property, parsed by
> > > of_get_regulation_constraints, which is called by
> > > regulator_of_get_init_data in the regulator core. And it appears in
> > > bindings/regulator/regulator.yaml. I believe the binding needs to be
> > > fixed, not the device trees.
> >
> > It's indeed parsed by the regulator framework, but then it calls into
> > the driver if that property is set using set_ramp_delay if it's set.
>
> Not only is it used for set_ramp_delay, but it's also used to calculate
> a post-change delay, see the following position (it can be overrided by
> a custom set_voltage_time in the driver):
>
> https://elixir.bootlin.com/linux/latest/source/drivers/regulator/core.c#L3339

Having just dug through the regulator core code at work, I agree.

Furthermore, the commit log for this addition specifically mentions the
reason for adding this property is to provide a (guessed) ramp rate for
the core to do a proper delay for the regulator to ramp up, not to set
the actual ramp rate in hardware.

ChenYu

[1] https://git.kernel.org/torvalds/c/fe79ea577be81e1e71642826ab00e676dc59c194

> >
> > https://elixir.bootlin.com/linux/latest/source/drivers/regulator/core.c#L1378
> >
> > We don't set that hook for the AXP806 DCDC-A and DCDC-E regulators
> > (that
> > use AXP_DESC_RANGES) at all:
> >
> > https://elixir.bootlin.com/linux/latest/source/drivers/regulator/axp20x-regulator.c#L343
> >
> > And the only implementation we have (set for AXP_DESC and AXP_DESC_IO)
> > works only for the AXP209:
> >
> > https://elixir.bootlin.com/linux/latest/source/drivers/regulator/axp20x-regulator.c#L368
> >
> > So, it just looks like those properties have never been tested since
> > they were just ignored.
> >
> > Maxime
> >
>
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