linux-kernel - Re: [PATCH v1 01/15] dt-bindings: add pwrseq device tree bindings

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Message-ID: <31792ef1-20b0-b801-23b7-29f303b91def@linaro.org>
Date:   Tue, 2 Nov 2021 18:26:45 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Stanimir Varbanov <svarbanov@...sol.com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:BLUETOOTH DRIVERS" <linux-bluetooth@...r.kernel.org>,
        ath10k@...ts.infradead.org,
        linux-wireless <linux-wireless@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v1 01/15] dt-bindings: add pwrseq device tree bindings

On 28/10/2021 00:53, Rob Herring wrote:
> On Tue, Oct 26, 2021 at 9:42 AM Dmitry Baryshkov
> <dmitry.baryshkov@...aro.org> wrote:
>>
>> On 26/10/2021 15:53, Rob Herring wrote:
>>> On Wed, Oct 06, 2021 at 06:53:53AM +0300, Dmitry Baryshkov wrote:
>>>> Add device tree bindings for the new power sequencer subsystem.
>>>> Consumers would reference pwrseq nodes using "foo-pwrseq" properties.
>>>> Providers would use '#pwrseq-cells' property to declare the amount of
>>>> cells in the pwrseq specifier.
>>>
>>> Please use get_maintainers.pl.
>>>
>>> This is not a pattern I want to encourage, so NAK on a common binding.
>>
>>
>> Could you please spend a few more words, describing what is not
>> encouraged? The whole foo-subsys/#subsys-cells structure?
> 
> No, that's generally how common provider/consumer style bindings work.
> 
>> Or just specifying the common binding?
> 
> If we could do it again, I would not have mmc pwrseq binding. The
> properties belong in the device's node. So don't generalize the mmc
> pwrseq binding.
> 
> It's a kernel problem if the firmware says there's a device on a
> 'discoverable' bus and the kernel can't discover it. I know you have
> the added complication of a device with 2 interfaces, but please,
> let's solve one problem at a time.

The PCI bus handling is a separate topic for now (as you have seen from 
the clearly WIP patches targeting just testing of qca6390's wifi part).

For me there are three parts of the device:
- power regulator / device embedded power domain.
- WiFi
- Bluetooth

With the power regulator being a complex and a bit nasty beast. It has 
several regulators beneath, which have to be powered up in a proper way.
Next platforms might bring additional requirements common to both WiFi 
and BT parts (like having additional clocks, etc). It is externally 
controlled (after providing power to it you have to tell, which part of 
the chip is required by pulling up the WiFi and/or BT enable GPIOs.

Having to duplicate this information in BT and WiFi cases results in 
non-aligned bindings (with WiFi and BT parts using different set of 
properties and different property names) and non-algined drivers (so the 
result of the powerup would depend on the order of drivers probing).

So far I still suppose that having a single separate entity controlling 
the powerup of such chips is the right thing to do.

I'd prefer to use the power-domain bindings (as the idea seems to be 
aligned here), but as the power-domain is used for the in-chip power 
domains, we had to invent the pwrseq name.

-- 
With best wishes
Dmitry