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

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Date:   Fri, 20 Aug 2021 21:06:53 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Andy Gross <agross@...nel.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

On Fri, 20 Aug 2021 at 20:01, Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
> On Fri 20 Aug 06:08 PDT 2021, Dmitry Baryshkov wrote:
>
> > Hi,
> >
> > On Thu, 19 Aug 2021 at 18:23, Marcel Holtmann <marcel@...tmann.org> wrote:
> > > > 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.
>
> It would be preferable if this was a implementation-only change and that
> we kept the existing binding and existing dtb continued to work.

This would require setting up the pwrseq from within the bt driver. I
did not have that in mind. However that'd ease the bt code, since we
won't have to handle the fallback/back-compatibility. Let me think
about it.

-- 
With best wishes
Dmitry