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 10:05:45 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Gregory CLEMENT <gregory.clement@...e-electrons.com>,
        Rob Herring <robh@...nel.org>
Cc:     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 22 November 2016 at 18:23, Gregory CLEMENT
<gregory.clement@...e-electrons.com> wrote:
> Hi Rob,
>
>  On jeu., nov. 10 2016, Ziji Hu <huziji@...vell.com> wrote:
>
> [...]
>
>>>> +
>>>> +- reg:
>>>> +  * For "marvell,xenon-sdhci", one register area for Xenon IP.
>>>> +
>>>> +  * For "marvell,armada-3700-sdhci", two register areas.
>>>> +    The first one for Xenon IP register. The second one for the Armada 3700 SOC
>>>> +    PHY PAD Voltage Control register.
>>>> +    Please follow the examples with compatible "marvell,armada-3700-sdhci"
>>>> +    in below.
>>>> +    Please also check property marvell,pad-type in below.
>>>> +
>>>> +Optional Properties:
>>>> +- marvell,xenon-slotno:
>>>
>>> Multiple slots should be represented as child nodes IMO. I think some
>>> other bindings already do this.
>>>
>>
>>       All the slots are entirely independent.
>>       I prefer to consider it as multiple independent SDHCs placed in
>>       a single IP, instead of that a IP contains multiple child slots.
>
> It was indeed what I tried to show in my answer for the 1st version:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2016-October/461860.html
>
> Maybe you missed it.
>
> 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

>
>>
>>       It is unlike the implementation which put multiple slots behind PCIe EP interface. sdhci-pci.c will handle each slot init one by one.
>>       If Xenon SDHC slots are represented as child nodes, there should also be a main entry in Xenon driver to init each child node one by one.
>>       In my very own opinion, it is inconvenient and unnecessary.
>

Kind regards
Uffe