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

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Message-ID: <YO8dnRE9pq5T64PD@yoga>
Date:   Wed, 14 Jul 2021 12:23:41 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Mark Brown <broonie@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-bluetooth@...r.kernel.org
Subject: Re: [PATCH v3 2/7] regulator: qca6390: add support for QCA639x
 powerup sequence

On Thu 08 Jul 05:09 CDT 2021, Ulf Hansson wrote:

> - Peter (the email was bouncing)
> 
> On Tue, 6 Jul 2021 at 13:55, Mark Brown <broonie@...nel.org> 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.
> 
> Therefore, I think it would be worth having a common solution for
> this, rather than a solution per subsystem or even worse, per device.
> 

Representing the chip and its power needs, separate from the busses does
seem reasonable. It's pretty much what Dmitry suggested originally, but
his attempts to use either power-domain or regulator references to
ensure ordering has been objected.


Beyond this, there is a similar case (that you and I have talked about
earlier) in supporting the SDX55 PCIe modem found in some devices.
Where in addition to ensuring that the power rails are configured, a
couple of gpios needs to be controlled and there's an incoming gpio line
indicating that the firmware of the device has locked up and the power
needs to be toggled and the device re-enumerated.

> Unfortunately, it looks like Peter's email is bouncing so we can't get
> an update from him.
> 

And for this second part, where we need some additional logic it seems
to go beyond what the power sequence discussions has touched upon so
far.

Regards,
Bjorn