linux-kernel - Re: [PATCH 5/10] dt: bindings: Add bindings for Marvell Xenon SD Host Controller

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Date:   Thu, 24 Nov 2016 10:11:19 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Gregory CLEMENT <gregory.clement@...e-electrons.com>,
        Rob Herring <robh@...nel.org>, Ziji Hu <huziji@...vell.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Jason Cooper <jason@...edaemon.net>,
        Andrew Lunn <andrew@...n.ch>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "Jack(SH) Zhu" <jmzhu@...vell.com>, Jimmy Xu <zmxu@...vell.com>,
        Jisheng Zhang <jszhang@...vell.com>,
        Nadav Haklai <nadavh@...vell.com>, Ryan Gao <ygao@...vell.com>,
        Doug Jones <dougj@...vell.com>,
        Shiwu Zhang <zhangshw@...vell.com>,
        Victor Gu <xigu@...vell.com>,
        "Wei(SOCP) Liu" <liuw@...vell.com>,
        Wilson Ding <dingwei@...vell.com>,
        Xueping Liu <xpliu@...vell.com>,
        Hilbert Zhang <zzhang@...vell.com>,
        Keji Zhang <keji@...vell.com>,
        Liuliu Zhao <zhaoliul@...vell.com>,
        Peng Zhu <zhupeng@...vell.com>, Yu Cao <yucao@...vell.com>,
        Romain Perier <romain.perier@...e-electrons.com>,
        Yehuda Yitschak <yehuday@...vell.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Hanna Hawa <hannah@...vell.com>,
        Kostya Porotchkin <kostap@...vell.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/10] dt: bindings: Add bindings for Marvell Xenon SD Host Controller

On Thursday, November 24, 2016 10:05:45 AM CET Ulf Hansson wrote:
> > You also mentioned other bindings using child nodes, but for this one
> > we have one controller with only one set of register with multiple slots
> > (Atmel is an example). Here each slot have it own set of register.
> >
> > Actually giving the fact that each slot is controlled by a different set
> > of register I wonder why the hardware can't also deduce the slot number
> > from the address register. For me it looks like an hardware bug but we
> > have to deal with it.
> >
> > Do you still think we needchild node here?
> 
> Using child-nodes for slots like what's done in the atmel case, is
> currently broken. I would recommend to avoid using child-nodes for
> slots, if possible.
> 
> To give you some more background, currently the mmc core treats child
> nodes as embedded non-removable cards or SDIO funcs. However, we can
> change to make child-nodes also allowed to describe slots, but it
> requires a specific compatible for "slots" and of course then we also
> need to update the DT parsing of the child-nodes in the mmc core.
> 
> Documentation/devicetree/bindings/mmc/mmc.txt
> Documentation/devicetree/bindings/mmc/mmc-card.txt

I don't see anything wrong with having child nodes for the slots
even with the current binding, under one condition:

The mmc.txt binding above must refer only to the child node, while
the parent node conceptually becomes a plain bus or MFD that
happens to encapsulate multiple MMC host controllers, and possibly
provides some shared registers to them.

	Arnd