linux-kernel - Re: [PATCH 01/11] mfd: add the Berlin controller driver

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Date:	Wed, 18 Feb 2015 11:58:53 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Cc:	Antoine Tenart <antoine.tenart@...e-electrons.com>,
	sameo@...ux.intel.com, jszhang@...vell.com, zmxu@...vell.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	arnd@...db.de
Subject: Re: [PATCH 01/11] mfd: add the Berlin controller driver

On Wed, 18 Feb 2015, Sebastian Hesselbarth wrote:

> On 18.02.2015 11:40, Lee Jones wrote:
> >On Wed, 18 Feb 2015, Antoine Tenart wrote:
> [...]
> >>chip: chip-controller@...000 {
> >>         compatible = "marvell,berlin2q-chip-ctrl", "syscon";
> >>         reg = <0xea0000 0x400>, <0xdd0170 0x10>;
> >>         #clock-cells = <1>;
> >>         clocks = <&refclk>;
> >>         clock-names = "refclk";
> >>
> >>         soc_pinctrl: pin-controller {
> >>                 compatible = "marvell,berlin2q-soc-pinctrl";
> >>
> >>                 twsi0_pmux: twsi0-pmux {
> >>                         groups = "G6";
> >>                         function = "twsi0";
> >>                 };
> >>
> >>                 twsi1_pmux: twsi1-pmux {
> >>                         groups = "G7";
> >>                         function = "twsi1";
> >>                 };
> >>         };
> >>
> >>         chip_rst: reset {
> >>                 compatible = "marvell,berlin2-reset";
> >>                 #reset-cells = <2>;
> >>         };
> >>};
> >
> >This is what I'd expect to see in DT, so we're heading in the right
> >direction.  So make to my original question, what's the point of this
> >MFD driver, and why don't you just let DT framework register these
> >devices for you?
> >
> >You issue a compatible string here, then duplicate it in the driver,
> >why do you think this is necessary?
> 
> there is no DT framework that automatically probes for
> compatible<->driver matches. You either make it "simple-bus" compatible
> which will call of_foo_populate() or you have to register each of the
> devices yourself. It clearly is not a bus, so if we use this as a
> workaround, we'll get yelled at by others.

I do agree that using 'simple-bus' to describe only this IP would be
an abuse.  However, my foundation thought/argument is unchanged.  This
'driver' is a hack.  It has no functional use besides to work around a
problem of semantics and as such has no place in MFD.

Back onto the simple-bus theme, as this is a syscon device it is a bus
of sorts.  Have you thought about making it a child of your its syscon
node, then using simple-bus to get the OF framework to register the
child devices?

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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