linux-kernel - Re: [PATCH v3 2/7] regulator: qca6390: add support for QCA639x powerup sequence

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAA8EJpoeYUOPLKca5oJNKdyOvOmoLX6FvsTbdmC7W9mLsyyVmw@mail.gmail.com>
Date:   Tue, 22 Jun 2021 19:46:08 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <linux-arm-msm@...r.kernel.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-bluetooth@...r.kernel.org
Subject: Re: [PATCH v3 2/7] regulator: qca6390: add support for QCA639x
 powerup sequence

On Tue, 22 Jun 2021 at 17:38, Mark Brown <broonie@...nel.org> wrote:
>
> On Tue, Jun 22, 2021 at 05:17:28PM +0300, Dmitry Baryshkov wrote:
> > On Tue, 22 Jun 2021 at 14:29, Mark Brown <broonie@...nel.org> wrote:
> > > On Tue, Jun 22, 2021 at 01:31:36AM +0300, Dmitry Baryshkov wrote:
>
> > > > Qualcomm QCA6390/1 is a family of WiFi + Bluetooth SoCs, with BT part
> > > > being controlled through the UART and WiFi being present on PCIe
> > > > bus. Both blocks share common power sources. Add device driver handling
> > > > power sequencing of QCA6390/1.
>
> > > Are you sure this is a regulator and not a MFD?  It appears to be a
> > > consumer driver that turns on and off a bunch of regulators en masse
> > > which for some reason exposes that on/off control as a single supply.
> > > This looks like it'd be much more appropriate to implement as a MFD or
> > > possibly power domain with the subdevices using runtime PM, it's clearly
> > > not a regulator.
>
> > First attempt was designed to be an MFD. And Lee clearly stated that
> > this is wrong:
> > "This is not an MFD, since it utilised neither the MFD API nor
> > of_platform_populate() to register child devices." [1]
>
> Well, perhaps it should do one of those things then?

I don't think so. BT part is just a serdev sitting on top of UART,
WiFi is PCIe device (for qca6390). So using MFD API (which primarily
targets platform devices) does not seem logical and feasible.

> Like I say this is
> very clearly not a regulator, it looks like a consumer of some kind.
> The regulator API isn't there just to absorb things that need reference
> counting, it's there to represent things providing supplies.  This seems
> to be very clearly not a supply given that it's grouping together a
> bunch of other supplies and switching them on and off together without
> providing a clear output supply.

Ack.

> > I've tried following Rob's suggestions on implementing things clearly,
> > but doing so results in too big restructure just for a single device.
>
> I don't know what that suggestion was?  If there's only one device that
> uses this why is it not implemented as part of that device?

One device = qca6390 (or 91). Because it is still a device sitting on
a PCI bus which is typically discoverable, while adding power
sequencer to the device driver would demand making the bus fully
descibiable (like PCI bus is on Spark).

> > > > +static int qca6390_enable(struct regulator_dev *rdev)
> > > > +{
> > > > +     struct qca6390_data *data = rdev_get_drvdata(rdev);
> > > > +     int ret;
>
> > > > +     ret = regulator_bulk_enable(data->num_vregs, data->regulators);
> > > > +     if (ret) {
> > > > +             dev_err(data->dev, "Failed to enable regulators");
> > > > +             return ret;
> > > > +     }
>
> > > The regulator API is *not* recursive, I am astonished this works.
>
> > It does, even with lockdep enabled. Moreover BT regularly does disable
> > and enable this regulator, so both enable and disable paths were well
> > tested.
> > Should I change this into some internal call to remove API recursiveness?
>
> You should not be implementing this as a regulator at all.

Ack

-- 
With best wishes
Dmitry