Re: [PATCH v3 2/7] regulator: qca6390: add support for QCA639x powerup sequence

[Ulf Hansson]

On Wed, 14 Jul 2021 at 18:47, Rob Herring <robh@xxxxxxxxxx> wrote:
>
> On Thu, Jul 08, 2021 at 02:37:44PM +0300, Dmitry Baryshkov wrote:
> > Hi,
> >
> > On Thu, 8 Jul 2021 at 13:10, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
> > >
> > > - Peter (the email was bouncing)
> >
> > + Peter's kernel.org address
> >
> > >
> > > On Tue, 6 Jul 2021 at 13:55, Mark Brown <broonie@xxxxxxxxxx> wrote:
> > > >
> > > > On Tue, Jul 06, 2021 at 09:54:03AM +0200, Ulf Hansson wrote:
> > > > > On Tue, 22 Jun 2021 at 00:32, Dmitry Baryshkov
> > > >
> > > > > > Qualcomm QCA6390/1 is a family of WiFi + Bluetooth SoCs, with BT part
> > > > > > being controlled through the UART and WiFi being present on PCIe
> > > > > > bus. Both blocks share common power sources. Add device driver handling
> > > > > > power sequencing of QCA6390/1.
> > > >
> > > > > Power sequencing of discoverable buses have been discussed several
> > > > > times before at LKML. The last attempt [1] I am aware of, was in 2017
> > > > > from Peter Chen. I don't think there is a common solution, yet.
> > > >
> > > > This feels a bit different to the power sequencing problem - it's not
> > > > exposing the individual inputs to the device but rather is a block that
> > > > manages everything but needs a bit of a kick to get things going (I'd
> > > > guess that with ACPI it'd be triggered via AML).  It's in the same space
> > > > but it's not quite the same issue I think, something that can handle
> > > > control of the individual resources might still struggle with this.
> > >
> > > Well, to me it looks very similar to those resouses we could manage
> > > with the mmc pwrseq, for SDIO. It's also typically the same kind of
> > > combo-chips that moved from supporting SDIO to PCIe, for improved
> > > performance I guess. More importantly, the same constraint to
> > > pre-power on the device is needed to allow it to be discovered/probed.
> >
> > In our case we'd definitely use pwrseq for PCIe bus and we can also
> > benefit from using pwrseq for serdev and for platform busses also (for
> > the same story of WiFi+BT chips).
> >
> > I can take a look at rewriting pwrseq code to also handle the PCIe
> > bus. Rewriting it to be a generic lib seems like an easy task,
> > plugging it into PCIe code would be more fun.
> >
> > Platform and serdev... Definitely even more fun.
>
> I don't want to see pwrseq (the binding) expanded to other buses. If
> that was the answer, we wouldn't be having this discussion. It was a
> mistake for MMC IMO.

Let's make sure we get your point correctly. I think we have discussed
this in the past, but let's refresh our memories.

If I recall correctly, you are against the mmc pwrseq DT bindings
because we are using a separate pwrseq OF node, that we point to via a
"mmc-pwrseq" property that contains a phandle from the mmc controller
device node. Is that correct?

If we would have encoded the power sequence specific properties, from
within a child node for the mmc controller node, that would have been
okay for you, right?

>
> If pwrseq works as a kernel library/api, then I have no issue with that.

That's what Peter Chen was trying to do. A generic interface, flexible
enough so it can be used for many similar configurations (but not
exactly the same).

Perhaps it was too generic though.

>
> >
> > > Therefore, I think it would be worth having a common solution for
> > > this, rather than a solution per subsystem or even worse, per device.
>
> Power sequencing requirements are inheritently per device unless we're
> talking about standard connectors.

The requirements are certainly per device, but the way to manage them
doesn't have to be.

As you said above, a generic library that subsystems/drivers can call
to power on/off a discoverable device, before trying to probe it would
be a good start.

>
> This is a solved problem on MDIO. It's quite simple. If there's a DT
> node for a device you haven't discovered, then probe it anyways.

A child OF node?

Then what do you think about some common power sequence properties
that we can use in such node?

>
> Rob

Kind regards
Uffe