linux-kernel - Re: [PATCH 2/4] mfd: qca639x: add support for QCA639x powerup sequence

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Date:   Tue, 22 Dec 2020 10:16:25 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        "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>
Subject: Re: [PATCH 2/4] mfd: qca639x: add support for QCA639x powerup
 sequence

On Mon, 21 Dec 2020, Dmitry Baryshkov wrote:

> Hello,
> 
> On Mon, 21 Dec 2020 at 12:02, Lee Jones <lee.jones@...aro.org> wrote:
> >
> > On Sun, 20 Dec 2020, Dmitry Baryshkov wrote:
> >
> > > Qualcomm QCA639x 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. So add mfd device driver
> > > handling power sequencing of QCA6390/1.
> > >
> > > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > > ---
> > >  drivers/mfd/Kconfig        |  12 +++
> > >  drivers/mfd/Makefile       |   1 +
> > >  drivers/mfd/qcom-qca639x.c | 168 +++++++++++++++++++++++++++++++++++++
> > >  3 files changed, 181 insertions(+)
> > >  create mode 100644 drivers/mfd/qcom-qca639x.c
> >
> > This is not an MFD, since it utilised neither the MFD API nor
> > of_platform_populate() to register child devices.
> 
> It would use them if the WiFi part was not on a discoverable bus.

This is a can of worms that I do not wish to open right now.

However the TL;DR is:

 MFD is currently only *meant* for non-discoverable platform devices.

> > Suggest you use drivers/power or similar to handle shared power
> > sequencing requirements.
> 
> What about drivers/soc/qcom? Or drivers/misc?

These are 2 other subsystems, just like MFD, which are commonly used
as dumping grounds for code which doesn't fit anywhere else.  However,
I implore you to please try to find a suitable subsystem for this to
fit into first.  If this driver only deals with power management,
place it is a power related subsystem *before* considering drivers/soc
or drivers/misc.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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