linux-kernel - Re: [RFC v2 00/13] create power sequencing subsystem

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Message-ID: <4a508fc1-6253-9c11-67fb-f84f17fd2719@kali.org>
Date:   Mon, 13 Sep 2021 18:39:55 -0500
From:   Steev Klimaszewski <steev@...i.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        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>
Cc:     linux-arm-msm@...r.kernel.org, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-bluetooth@...r.kernel.org,
        ath10k@...ts.infradead.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [RFC v2 00/13] create power sequencing subsystem


On 8/29/21 8:12 AM, Dmitry Baryshkov wrote:
> This is the second RFC on 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.
>
> To ease migration to pwrseq and to provide compatibility with older
> device trees, while keeping drivers simple, this iteration of RFC
> introduces pwrseq fallback support: pwrseq driver can register fallback
> providers. If another device driver requests pwrseq instance and none
> was declared, the pwrseq fallback code would go through the list of
> fallback providers and if the match is found, driver would return a
> crafted pwrseq instance. For now this mechanism is limited to the OF
> device matching, but it can be extended further to use any combination
> of device IDs.
>
> 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 or
> serial + SDIO 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 bus scan depending on the proper
>    device structure in the device tree.
>
> Changes since RFC v1:
>  - Provider pwrseq fallback support
>  - Implement fallback support in pwrseq_qca.
>  - Mmove susclk handling to pwrseq_qca.
>  - Significantly simplify hci_qca.c changes, by dropping all legacy
>    code. Now hci_qca uses only pwrseq calls to power up/down bluetooth
>    parts of the chip.
>
I tested this here, on the Lenovo Yoga C630, after creating a patch to
do basically the same thing as the db845c does.  One thing I noticed, if
PWRSEQ=y and the rest are =m, there is a build error.  I suppose once
the full set is posted and not RFC, I can send the patch for that. 

One question I have, if you don't mind, in patch 11, you add a second
channel to qca power sequencer.  I've added that here, but in the c630's
dts, "vreg_l23a_3p3: ldo23" is empty, so I added the same numbers in for
the regulator, and I'm wondering how to test that it's actually working
correctly?

-- steev