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

From: Lee Jones <lee.jones@linaro.org>
To: Andrew Lunn <andrew@lunn.ch>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>,
	Rob Herring <robh+dt@kernel.org>,
	devicetree@vger.kernel.org,
	Kunihiko Hayashi <hayashi.kunihiko@socionext.com>,
	Felipe Balbi <felipe.balbi@linux.intel.com>,
	linux-usb@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Jassi Brar <jaswinder.singh@linaro.org>,
	Masami Hiramatsu <masami.hiramatsu@linaro.org>,
	Arnd Bergmann <arnd@arndb.de>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [Question] MFD driver that handles clocks/resets and populates child nodes
Date: Tue, 3 Apr 2018 09:03:35 +0100	[thread overview]
Message-ID: <20180403080335.ksekhxwvbzbxhmln@dell> (raw)
In-Reply-To: <20180402133219.GA10520@lunn.ch>

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@lunn.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?

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