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

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Message-ID: <3bab8bd8c69a878f849a07dd9ea35bfac2006da2.camel@fi.rohmeurope.com>
Date:   Wed, 2 Dec 2020 13:32:14 +0000
From:   "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>
To:     "lee.jones@...aro.org" <lee.jones@...aro.org>
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

Hello Lee,

On Wed, 2020-12-02 at 12:57 +0000, Lee Jones wrote:
> 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.

Yes. And it is described. But I've occasionally received request from
DT guys to add some properties directly to MFD node and not to add own
sub-node. This is what is done for example with the BD71837/47 clocks -
there is no own node for clk - the clk properties are placed directly
in MFD node (as was requested by Stephen and Rob back then - I
originally had own node for clk). I really have no clear view on when
things warrant for own subnode and when they don't - but as far as I
can see using simple-mfd-i2c forces one to always have a sub-node /
device. Even just a empty node with nothing but the compatible even if
device does not need stuff from DT? Anyways, I think this is nice
addition for simple drivers.

> > 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?

Yes. I planned to use regmap-irq and create irq chip in MFD when the
over / under voltage / temperature - notifications or watchdog IRQs are
needed. 

Best Regards,
	Matti Vaittinen