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

From: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
To: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
	Rob Herring <robh@kernel.org>
Cc: Andy Gross <agross@kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Marcel Holtmann <marcel@holtmann.org>,
	Johan Hedberg <johan.hedberg@gmail.com>,
	Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
	Kalle Valo <kvalo@codeaurora.org>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Stanimir Varbanov <svarbanov@mm-sol.com>,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	linux-mmc <linux-mmc@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"open list:BLUETOOTH DRIVERS" <linux-bluetooth@vger.kernel.org>,
	ath10k@lists.infradead.org,
	linux-wireless <linux-wireless@vger.kernel.org>,
	netdev <netdev@vger.kernel.org>, Abel Vesa <abel.vesa@linaro.org>
Subject: Re: [PATCH v1 01/15] dt-bindings: add pwrseq device tree bindings
Date: Fri, 10 Mar 2023 07:56:49 +0000	[thread overview]
Message-ID: <6108c68b-e38b-3060-f6fa-53be79a795d7@linaro.org> (raw)
In-Reply-To: <31792ef1-20b0-b801-23b7-29f303b91def@linaro.org>

On 02/11/2021 15:26, Dmitry Baryshkov wrote:
> On 28/10/2021 00:53, Rob Herring wrote:
>> On Tue, Oct 26, 2021 at 9:42 AM Dmitry Baryshkov
>> <dmitry.baryshkov@linaro.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.

Just to keep this topic updated with some pointers [1] to changes done 
to solve same problem in USB Hub. These patches 
(drivers/usb/misc/onboard_usb_hub*) have been merged since last year July.

It looks like we can take some inspiration from this to address PCIE Bus 
issue aswell.

Thanks to Neil to point this.

[1] 
https://lore.kernel.org/lkml/20220630193530.2608178-1-mka@chromium.org/T/

--srini
> 
> 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.
> 