linux-kernel - Re: [PATCH v8 16/17] PCI/pwrctl: add a PCI power control driver for power sequenced devices

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Message-ID: <CAMRc=MehAkEGJmCXi1uad1f7jZAT60OQ2N0jX7AMka4rS9OjDg@mail.gmail.com>
Date: Wed, 5 Jun 2024 20:04:15 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, Liam Girdwood <lgirdwood@...il.com>, 
	Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Marcel Holtmann <marcel@...tmann.org>, Luiz Augusto von Dentz <luiz.dentz@...il.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Balakrishna Godavarthi <quic_bgodavar@...cinc.com>, Rocky Liao <quic_rjliao@...cinc.com>, 
	Kalle Valo <kvalo@...nel.org>, Jeff Johnson <jjohnson@...nel.org>, 
	Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konrad.dybcio@...aro.org>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Srini Kandagatla <srinivas.kandagatla@...aro.org>, 
	Elliot Berman <quic_eberman@...cinc.com>, Caleb Connolly <caleb.connolly@...aro.org>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Alex Elder <elder@...nel.org>, 
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-bluetooth@...r.kernel.org, 
	netdev@...r.kernel.org, linux-wireless@...r.kernel.org, 
	ath11k@...ts.infradead.org, Jeff Johnson <quic_jjohnson@...cinc.com>, 
	ath12k@...ts.infradead.org, linux-pm@...r.kernel.org, 
	linux-pci@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, kernel@...cinc.com, 
	Amit Pundir <amit.pundir@...aro.org>
Subject: Re: [PATCH v8 16/17] PCI/pwrctl: add a PCI power control driver for
 power sequenced devices

On Wed, Jun 5, 2024 at 7:47 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> > >
> > >   wifi@0 {
> > >     compatible = "pci17cb,1101", "wlan-pwrseq";
> >
> > What even is "pwrseq" in the context of the hardware description? DT
> > maintainers would like to have a word with you. :)
>
> There are "compatible" strings like "simple-bus", "simple-mfd", and
> "syscon" that allow drivers to bind and provide generic functionality
> when they don't need to know the exact hardware.
>

There's a difference however: a "simple bus" is a thing. A "simple
multifunction device" is also an actual thing. A "pwrseq" or
"power-sequencer" is not a thing, it's a functionality. And we don't
describe it in device-tree. Rob has said before that he regrets having
merged the mmc pwrseq bindings back in the day and that he wouldn't do
it again now because it describes what HW does and not what it is. In
this case the PMU is simply a PMIC and the bindings I'm proposing
describe it as such. But what you're proposing is even worse: this is
the ath1x module of the larger chipset (power sequencee rather than
sequencer) so naming it "wlan-pwrseq" makes absolutely no sense at
all. It's a PCI device whose ID is 0x17cb1101 and the device tree
describes it as such.

> > > and pci_pwrctl_pwrseq_of_match[] had this:
> > >
> > >   { .compatible = "wlan-pwrseq", .data = "wlan", }
> > >
> > > Wouldn't this pci-pwrctl-pwrseq driver work the same?  I'm not a DT
> > > whiz, so likely I'm missing something, but it would be nice if we
> > > didn't have to update this very generic-looking driver to add every
> > > device that needs it.
>
> Do you have any other ideas to reduce the churn in this file?  It just
> seems weird to have to add an ID to this file without adding any
> actual code or data related to it.
>

Is it really that much churn though? You'd save 4 lines of code? I
think this is premature optimization, we'll see about unifying it when
we have several models supported, right now with two, I'd just leave
it as is and not seek perfection.

> We should probably also add a pattern to MAINTAINERS so
> get_maintainers.pl on this file will show you as a maintainer.
>

Makes sense.

Bartosz

> Bjorn