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

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Date: Mon, 19 Feb 2024 18:18:28 +0100
From: neil.armstrong@...aro.org
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Bartosz Golaszewski <brgl@...ev.pl>
Cc: 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 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.

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.

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.
> 
>