linux-kernel - Re: [Question] MFD driver that handles clocks/resets and populates child nodes

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Date:   Tue, 3 Apr 2018 13:59:53 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Andrew Lunn <andrew@...n.ch>, Rob Herring <robh+dt@...nel.org>,
        devicetree@...r.kernel.org,
        Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        linux-usb@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jassi Brar <jaswinder.singh@...aro.org>,
        Masami Hiramatsu <masami.hiramatsu@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Question] MFD driver that handles clocks/resets and populates
 child nodes

On Tue, 03 Apr 2018, Masahiro Yamada wrote:

> 2018-04-03 17:03 GMT+09:00 Lee Jones <lee.jones@...aro.org>:
> > On Mon, 02 Apr 2018, Andrew Lunn wrote:
> >
> >> On Mon, Apr 02, 2018 at 10:21:01PM +0900, Masahiro Yamada wrote:
> >> > 2018-04-02 21:04 GMT+09:00 Andrew Lunn <andrew@...n.ch>:
> >> > >> The maintainer of DWC3, Felipe Balbi, requested to
> >> > >> split the glue layer driver into small parts such as
> >> > >> reset, regulator, phy, etc.
> >> > >
> >> > > What exactly did Felipe ask for? Did he ask that the patch be split
> >> > > up, one patch per reset, regulator, phy etc?
> >> >
> >> >
> >> > Yeah.  That is what we understood from his comments.
> >> >
> >> >
> >> > These are the feed-backs from him.
> >> >
> >> > https://lkml.org/lkml/2018/1/23/298
> >> > https://lkml.org/lkml/2018/1/24/352
> >>
> >> > > Are all these resources used just by the DWC3? Or is it a true MFD,
> >> > > multiple functions?
> >> >
> >> > I do not think this is a real MFD.
> >> >
> >> > This is a DWC3 glue layer, i.e.
> >> > a collection of misc registers that control
> >> > the DWC3 IP.
> >> >
> >> >
> >> > Just splitting it into small pieces
> >> > to use PHY, reset, regulator framework in Linux.
> >> >
> >> > Of course, the price of this approach
> >> > is so cluttered Device Tree,
> >> > honestly I do not like it much.
> >>
> >> This however the correct way to do this. You should have a phy driver,
> >> and a regulator driver, and a reset driver. The DWC3 then uses
> >> phandles to these drivers.
> >>
> >> How is the IO map area 65b00000 split up. Can you cleanly separate it
> >> into sub areas, which do not overlap, so you have a sub-area for the
> >> PHY driver, a sub-area for the regulator driver and a sub-area for the
> >> reset area? If you can cleanly split it up, you don't need an MFD. If
> >> however the registers are in overlapping areas, you do need an
> >> MFD. The MFD core provides access to the registers, while its children
> >> implement PHY, reset, regulator etc.
> >
> > This device certainly sounds like an MFD to me.
> >
> > Can you share the DT you've written please?
> 
> 
> This is still under the internal review in Socionext,
> but I attached it below FWIW.
> 
> (I am not the author of this DT.
>  Written by Kunihiko Hayashi,
> 
> Just skimming the driver, I guess it will be possible to flatten
> the node structure by separating the register space into sub-areas.
> If this is success, we do not the MFD driver.

Sounds like a plan.  Pretty sure this isn't really an MFD.

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