netdev - Re: [RFC PATCH 00/15] create power sequencing subsystem

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Message-Id: <551758F2-0B00-4DEB-92C9-37472E46B75D@holtmann.org>
Date:   Sat, 21 Aug 2021 08:50:40 +0200
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.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>,
        MSM <linux-arm-msm@...r.kernel.org>, linux-mmc@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        "open list:BLUETOOTH SUBSYSTEM" <linux-bluetooth@...r.kernel.org>,
        ath10k@...ts.infradead.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [RFC PATCH 00/15] create power sequencing subsystem

Hi Dmitry,

>>> This is an RFC of the proposed power sequencer subsystem. This is a
>>> generification of the MMC pwrseq code. The subsystem tries to abstract
>>> the idea of complex power-up/power-down/reset of the devices.
>>> 
>>> The primary set of devices that promted me to create this patchset is
>>> the Qualcomm BT+WiFi family of chips. They reside on serial+platform
>>> interfaces (older generations) or on serial+PCIe (newer generations).
>>> They require a set of external voltage regulators to be powered on and
>>> (some of them) have separate WiFi and Bluetooth enable GPIOs.
>>> 
>>> This patchset being an RFC tries to demonstrate the approach, design and
>>> usage of the pwrseq subsystem. Following issues are present in the RFC
>>> at this moment but will be fixed later if the overall approach would be
>>> viewed as acceptable:
>>> 
>>> - No documentation
>>> While the code tries to be self-documenting proper documentation
>>> would be required.
>>> 
>>> - Minimal device tree bindings changes
>>> There are no proper updates for the DT bindings (thus neither Rob
>>> Herring nor devicetree are included in the To/Cc lists). The dt
>>> schema changes would be a part of v1.
>>> 
>>> - Lack of proper PCIe integration
>>> At this moment support for PCIe is hacked up to be able to test the
>>> PCIe part of qca6390. Proper PCIe support would require automatically
>>> powering up the devices before the scan basing on the proper device
>>> structure in the device tree.
>>> 
>>> ----------------------------------------------------------------
>>> Dmitry Baryshkov (15):
>>>    power: add power sequencer subsystem
>>>    pwrseq: port MMC's pwrseq drivers to new pwrseq subsystem
>>>    mmc: core: switch to new pwrseq subsystem
>>>    ath10k: add support for pwrseq sequencing
>>>    Bluetooth: hci_qca: merge qca_power into qca_serdev
>>>    Bluetooth: hci_qca: merge init paths
>>>    Bluetooth: hci_qca: merge qca_power_on with qca_regulators_init
>>>    Bluetooth: hci_qca: futher rework of power on/off handling
>>>    Bluetooth: hci_qca: add support for pwrseq
>> 
>> any chance you can try to abandon patching hci_qca. The serdev support in hci_uart is rather hacking into old line discipline code and it is not aging well. It is really becoming a mess.
> 
> I wanted to stay away from rewriting the BT code. But... New driver
> would have a bonus point that I don't have to be compatible with old
> bindings. In fact we can even make it the other way around: let the
> old driver always use regulators and make the new driver support only
> the pwrseq. Then it should be possible to drop the old hci_qca driver
> together with dropping the old bindings.
> 
>> I would say that the Qualcomm serial devices could use a separate standalone serdev driver. A while I send an RFC for a new serdev driver.
>> 
>> https://www.spinics.net/lists/linux-bluetooth/msg74918.html
> 
> Any reason why your driver stayed as an RFC and never made it into the
> kernel? Do you plan to revive your old RFCs on H:4 and H:5?

I was missing enough hardware to test it on and frankly I hoped that someone would pick up this work. The HCI line discipline “hack” needs to be removed soon. It is complicated, cumbersome and has a bunch of issues with locking. Mind you that originated in 2.4.6 kernel and is at its core bit-rotting.

If you manage to put QCA support into a separate btqcauart driver, that would be awesome. The btmtkuart driver is another example where Mediatek got its own serdev based driver.

Regards

Marcel