linux-kernel - Re: [PATCH RESEND v6 2/4] mfd: Support ROHM BD9576MUF and BD9573MUF

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Date:   Wed, 2 Dec 2020 12:57:23 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>
Cc:     "linux@...ck-us.net" <linux@...ck-us.net>,
        "wim@...ux-watchdog.org" <wim@...ux-watchdog.org>,
        "mazziesaccount@...il.com" <mazziesaccount@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        linux-power <linux-power@...rohmeurope.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
Subject: Re: [PATCH RESEND v6 2/4] mfd: Support ROHM BD9576MUF and BD9573MUF

On Fri, 27 Nov 2020, Vaittinen, Matti wrote:

> Hello Lee,
> 
> On Fri, 2020-11-27 at 08:32 +0000, Lee Jones wrote:
> > On Mon, 23 Nov 2020, Matti Vaittinen wrote:
> > 
> > > Add core support for ROHM BD9576MUF and BD9573MUF PMICs which are
> > > mainly used to power the R-Car series processors.
> > > 
> > > Signed-off-by: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
> > > ---
> > >  drivers/mfd/Kconfig              |  11 ++++
> > >  drivers/mfd/Makefile             |   1 +
> > >  drivers/mfd/rohm-bd9576.c        | 108
> > > +++++++++++++++++++++++++++++++
> > >  include/linux/mfd/rohm-bd957x.h  |  59 +++++++++++++++++
> > >  include/linux/mfd/rohm-generic.h |   2 +
> > >  5 files changed, 181 insertions(+)
> > >  create mode 100644 drivers/mfd/rohm-bd9576.c
> > >  create mode 100644 include/linux/mfd/rohm-bd957x.h
> > 
> > Looks like a possible candidate for "simple-mfd-i2c".
> > 
> > Could you look into that please?
> > 
> I must admit I didn't know about "simple-mfd-i2c". Good thing to know
> when working with simple devices :) Is this a new thing?

Yes, it's new.

> I am unsure I understand the idea fully. Should users put all the
> different regamp configs in this file and just add the device IDs with
> pointer to correct config? (BD9576 and BD9573 need volatile ranges).
> Also, does this mean each sub-device should have own node and own
> compatible in DT to get correctly load and probed? I guess this would
> need a buy-in from Rob too then.

You should describe the H/W in DT.

> By the way - for uneducated eyes like mine this does not look like it
> has much to do with MFD as a device - here MFD reminds me of a simple-
> bus on top of I2C.

This is for MFD devices where the parent does little more than create
a shared address space for child devices to operate on - like yours.

> Anyways, the BD9576 and BD9573 both have a few interrupts for OVD/UVD
> conditions and I am expecting that I will be asked to provide the
> regulator notifiers for those. Reason why I omitted the IRQs for now is
> that the HW is designed to keep the IRQ asserted for whole error
> duration so some delayed ack mechanism would be needed. I would like to
> keep the door open for adding IRQs to MFD core.

You mean to add an IRQ Domain?

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