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

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Date:   Fri, 20 Aug 2021 16:08:21 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Marcel Holtmann <marcel@...tmann.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,

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. 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?

> There I had the idea that simple vendor specifics can be in that driver (like the Broadcom part I added there), but frankly the QCA specifics are a bit too specific and it should be a separate driver. However I think this would be a good starting point.
>
> In general a H:4 based Bluetooth driver is dead simple with the help of h4_recv.h helper we have in the kernel. The complicated part is the power management pieces or any vendor specific low-power protocol they are running on that serial line. And since you are touching this anyway, doing a driver from scratch might be lot simpler and cleaner. It would surely help all the new QCA device showing up in the future.

-- 
With best wishes
Dmitry