linux-kernel - Re: [PATCH v4 03/10] pinctrl: mvebu: kirkwood pinctrl driver

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Date:	Mon, 17 Sep 2012 08:36:28 +0200
From:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
To:	Nicolas Pitre <nico@...xnic.net>
CC:	Jason Cooper <jason@...edaemon.net>, Andrew Lunn <andrew@...n.ch>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Lior Amsalem <alior@...vell.com>,
	Russell King <linux@....linux.org.uk>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Rob Herring <rob.herring@...xeda.com>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	devicetree-discuss@...ts.ozlabs.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 03/10] pinctrl: mvebu: kirkwood pinctrl driver

On 09/17/2012 03:55 AM, Nicolas Pitre wrote:
> On Sun, 16 Sep 2012, Jason Cooper wrote:
>> On Sun, Sep 16, 2012 at 09:46:52AM +0200, Andrew Lunn wrote:
>>>> +++ b/Documentation/devicetree/bindings/pinctrl/marvell,kirkwood-pinctrl.txt
>>>> @@ -0,0 +1,279 @@
>>>> +* Marvell Kirkwood SoC pinctrl driver for mpp
>>>> +
>>>> +Please refer to marvell,mvebu-pinctrl.txt in this directory for common binding
>>>> +part and usage.
>>>> +
>>>> +Required properties:
>>>> +- compatible: "marvell,88f6180-pinctrl",
>>>> +              "marvell,88f6190-pinctrl", "marvell,88f6192-pinctrl",
>>>> +              "marvell,88f6281-pinctrl", "marvell,88f6282-pinctrl"
>>>> +
>>>> +This driver supports all kirkwood variants, i.e. 88f6180, 88f619x, and 88f628
 >>> ...
>>> If i wanted to mass convert all existing kirkwood DT boards over to
>>> use pinctrl, im stuck at the very first step. I've no idea what chip
>>> they use, it was not relevant before.
>>
>> Let's try to do the DT correctly, and create a migration path for
>> kirkwood to work first, then migrate to using the DT fully.
>
> Beware beware.
>
> The DT should of course describe the hardware as accurately as possible.
> That doesn't necessarily mean it should describe the hardware as
> _extensively_ as possible.
>
> And that doesn't mean that all the information found in the DT has to be
> consumed by the kernel either.
>
> Any information that can be *probed* at run time has no benefit being
> stuffed in a DT.  That's true whether it is Linux or another operating
> system.  The more that can be probed at run time the better.

I had a closer look at how kirkwood probes its id. I mentionend kirkwood_id()
earlier but in fact it is kirkwood_pcie_id(). I assume pcie registers are shut
down with pcie clk gated? That would require to have pcie running at least at
boot-time on all boards.

While it is still possible to grab the id and power down pcie later, I still
think that using five different compatible strings is better here. Of course,
there is some effort to obtain the kirkwood SoC variant for all boards.

Sebastian




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