linux-kernel - Re: [PATCH] memory: add a basic OF-based memory driver

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Date:	Mon, 16 Sep 2013 07:55:29 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Grant Likely <grant.likely@...aro.org>
Cc:	Olof Johansson <olof@...om.net>,
	Emilio López <emilio@...pez.com.ar>,
	Mike Turquette <mturquette@...aro.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Rob Herring <rob.herring@...xeda.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	David Lanzendörfer <david.lanzendoerfer@....ch>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] memory: add a basic OF-based memory driver

On Sun, Sep 15, 2013 at 7:43 AM, Grant Likely <grant.likely@...aro.org> wrote:
> On Fri, 13 Sep 2013 08:49:06 -0700, Olof Johansson <olof@...om.net> wrote:
>> On Fri, Sep 13, 2013 at 7:00 AM, Rob Herring <robherring2@...il.com> wrote:
>> > On Thu, Sep 12, 2013 at 8:31 PM, Emilio López <emilio@...pez.com.ar> wrote:

[snip]

>> > Better, but this is still wrong. DT describes the hardware. There is
>> > no such h/w as a simple-memory-controller. The fact that you have a
>> > simple-memory-ctrlr kernel driver is a kernel
>> > feature/artifact/limitation. Describe the h/w with a meaningful
>> > compatible string and put that string in the simple memory controller
>> > driver match table. If someday we have a real driver for said memory
>> > controller, then it is only a kernel change to use a different driver.
>>
>>
>> We discussed this over IRC last night -- I still think it makes more
>> sense to make the clock driver for sunxi aware of this and just add a
>> reference to the clock at init time.
>>
>> This is never going to differ from board to board (today the clock
>> name is the same on all sunxi platforms -- pll5_ddr. And the need will
>> likewise be there for all platforms at this time.
>>
>> If and when it changes in the future, we can reevaluate. But this
>> doesn't have to be driven by device tree at this time, it seems to
>> just make things overly complicated and contrived.
>
> I agree. Creating a new platform driver + device tree binding just to
> claim a clock that must not be disables does not look like the right
> approach to me either.

Maybe a driver is overkill, but fully describing the h/w would be a
good thing. Only defining the h/w that Linux currently uses is not a
good practice (although admittedly hard to avoid).

Rob
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