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

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Message-ID: <CAL_JsqJACEtSRaDg0TcYODzhpsHFGa4mFSYa_R3qspypEKH+hQ@mail.gmail.com>
Date:	Fri, 13 Sep 2013 09:00:48 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Emilio López <emilio@...pez.com.ar>
Cc:	Olof Johansson <olof@...om.net>,
	Mike Turquette <mturquette@...aro.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Grant Likely <grant.likely@...aro.org>,
	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 Thu, Sep 12, 2013 at 8:31 PM, Emilio López <emilio@...pez.com.ar> wrote:
> Hi Olof,
>
> El 12/09/13 21:57, Olof Johansson escribió:
>
>> On Thu, Sep 12, 2013 at 5:30 PM, Emilio López <emilio@...pez.com.ar>
>> wrote:
>>>
>>> This driver's only job is to claim and ensure the necessary clock
>>> for memory operation on a DT-powered machine remains enabled.
>>>
>>> Signed-off-by: Emilio López <emilio@...pez.com.ar>
>>> ---
>>>
>>> I believe this new patch should resolve all the concerns raised; as
>>> always, all feedback is welcome :)
>>
>>
>> I think you're going about this the wrong way.
>>
>> If you have a problem with a clock not staying on, shouldn't you just
>> marking it appropriately in the clock table instead, making sure it's
>> initialized with at least one reference to it?
>
>
> If by "the clock table" you mean the tree as handled by the common clock
> framework, there is no such flag available as of today; see Mike's reply for
> more information.
>
> Personally I feel that if the general case can solve our problems (in this
> case, having a consumer who prepares and enables the clock), we should avoid
> adding special cases to the framework.
>
>
>> I believe that is how
>> some of the other platforms handle this, and it's a lot cleaner than
>> adding a fake binding and a fake driver just to grab a single clock.
>
>
> The binding doesn't have to be fake; it is actually describing the memory
> controller hardware:
>
> mc: mc@...3000 {
>         compatible = "simple-memory-controller";
>         reg = <0x0123000 0x400>;
>         clocks = <&pll5 1>;
> };
>
> If one day we get docs and/or have any special features we may need from the
> controller, we can use something like
>
> mc: mc@...3000 {
>         compatible = "vendor,awesome-mc", "simple-memory-controller";
>         reg = <0x0123000 0x400>;
>         clocks = <&pll5 1>;
> };

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.

Rob
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