linux-kernel - Re: [PATCH v5 00/18] power: sequencing: implement the subsystem and add first users

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Message-ID: <CAA8EJppWY8c-pF75WaMadWtEuaAyCc5A1VLEq=JmB2Ngzk-zyw@mail.gmail.com>
Date: Tue, 20 Feb 2024 00:21:45 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: neil.armstrong@...aro.org
Cc: Bartosz Golaszewski <brgl@...ev.pl>, 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>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, 
	Conor Dooley <conor+dt@...nel.org>, Kalle Valo <kvalo@...nel.org>, 
	Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konrad.dybcio@...aro.org>, 
	Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Saravana Kannan <saravanak@...gle.com>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, Arnd Bergmann <arnd@...db.de>, 
	Marek Szyprowski <m.szyprowski@...sung.com>, Alex Elder <elder@...aro.org>, 
	Srini Kandagatla <srinivas.kandagatla@...aro.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Abel Vesa <abel.vesa@...aro.org>, 
	Manivannan Sadhasivam <mani@...nel.org>, Lukas Wunner <lukas@...ner.de>, linux-bluetooth@...r.kernel.org, 
	netdev@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-pci@...r.kernel.org, linux-pm@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v5 00/18] power: sequencing: implement the subsystem and
 add first users

On Mon, 19 Feb 2024 at 19:18, <neil.armstrong@...aro.org> wrote:
>
> On 19/02/2024 13:33, Dmitry Baryshkov wrote:
> > On Mon, 19 Feb 2024 at 14:23, Bartosz Golaszewski <brgl@...ev.pl> wrote:
> >>
> >> On Mon, Feb 19, 2024 at 11:26 AM Dmitry Baryshkov
> >> <dmitry.baryshkov@...aro.org> wrote:
> >>>
> >>
> >> [snip]
> >>
> >>>>>>>>
> >>>>>>>> For WCN7850 we hide the existence of the PMU as modeling it is simply not
> >>>>>>>> necessary. The BT and WLAN devices on the device-tree are represented as
> >>>>>>>> consuming the inputs (relevant to the functionality of each) of the PMU
> >>>>>>>> directly.
> >>>>>>>
> >>>>>>> We are describing the hardware. From the hardware point of view, there
> >>>>>>> is a PMU. I think at some point we would really like to describe all
> >>>>>>> Qualcomm/Atheros WiFI+BT units using this PMU approach, including the
> >>>>>>> older ath10k units present on RB3 (WCN3990) and db820c (QCA6174).
> >>>>>>
> >>>>>> While I agree with older WiFi+BT units, I don't think it's needed for
> >>>>>> WCN7850 since BT+WiFi are now designed to be fully independent and PMU is
> >>>>>> transparent.
> >>>>>
> >>>>> I don't see any significant difference between WCN6750/WCN6855 and
> >>>>> WCN7850 from the PMU / power up point of view. Could you please point
> >>>>> me to the difference?
> >>>>>
> >>>>
> >>>> The WCN7850 datasheet clearly states there's not contraint on the WLAN_EN
> >>>> and BT_EN ordering and the only requirement is to have all input regulators
> >>>> up before pulling up WLAN_EN and/or BT_EN.
> >>>>
> >>>> This makes the PMU transparent and BT and WLAN can be described as independent.
> >>>
> >>>  From the hardware perspective, there is a PMU. It has several LDOs. So
> >>> the device tree should have the same style as the previous
> >>> generations.
> >>>
> >>
> >> My thinking was this: yes, there is a PMU but describing it has no
> >> benefit (unlike QCA6x90). If we do describe, then we'll end up having
> >> to use pwrseq here despite it not being needed because now we won't be
> >> able to just get regulators from WLAN/BT drivers directly.
> >>
> >> So I also vote for keeping it this way. Let's go into the package
> >> detail only if it's required.
> >
> > The WiFi / BT parts are not powered up by the board regulators. They
> > are powered up by the PSU. So we are not describing it in the accurate
> > way.
>
> I disagree, the WCN7850 can also be used as a discrete PCIe M.2 card, and in
> this situation the PCIe part is powered with the M.2 slot and the BT side
> is powered separately as we currently do it now.

QCA6390 can also be used as a discrete M.2 card.

> So yes there's a PMU, but it's not an always visible hardware part, from the
> SoC PoV, only the separate PCIe and BT subsystems are visible/controllable/powerable.

>From the hardware point:
- There is a PMU
- The PMU is connected to the board supplies
- Both WiFi and BT parts are connected to the PMU
- The BT_EN / WLAN_EN pins are not connected to the PMU

So, not representing the PMU in the device tree is a simplification.

>
> Neil
>
> >
> > Moreover, I think we definitely want to move BT driver to use only the
> > pwrseq power up method. Doing it in the other way results in the code
> > duplication and possible issues because of the regulator / pwrseq
> > taking different code paths.

-- 
With best wishes
Dmitry