Re: [PATCH v7 5/5] ARM: OMAP: gpmc: add DT bindings for GPMC timings and NAND

[Jon Hunter <jon-hunter-l0cyMroinI0@public.gmane.org>]

On 12/05/2012 05:24 PM, Grant Likely wrote:
> On Wed, 5 Dec 2012 16:33:48 -0600, Jon Hunter <jon-hunter-l0cyMroinI0@public.gmane.org> wrote:
>> Hi Grant,
>>
>> On 12/05/2012 04:22 PM, Grant Likely wrote:
>>> On Wed,  5 Dec 2012 20:09:31 +0100, Daniel Mack <zonque-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>>>> This patch adds basic DT bindings for OMAP GPMC.
>>>>
>>>> The actual peripherals are instantiated from child nodes within the GPMC
>>>> node, and the only type of device that is currently supported is NAND.
>>>>
>>>> Code was added to parse the generic GPMC timing parameters and some
>>>> documentation with examples on how to use them.
>>>>
>>>> Successfully tested on an AM33xx board.
>>>>
>>>> Signed-off-by: Daniel Mack <zonque-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>>>> ---
>>>>  Documentation/devicetree/bindings/bus/ti-gpmc.txt  |  77 ++++++++++
>>>>  .../devicetree/bindings/mtd/gpmc-nand.txt          |  76 +++++++++
>>>>  arch/arm/mach-omap2/gpmc.c                         | 171 ++++++++++++++++++++-
>>>>  3 files changed, 323 insertions(+), 1 deletion(-)
>>>>  create mode 100644 Documentation/devicetree/bindings/bus/ti-gpmc.txt
>>>>  create mode 100644 Documentation/devicetree/bindings/mtd/gpmc-nand.txt
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/bus/ti-gpmc.txt b/Documentation/devicetree/bindings/bus/ti-gpmc.txt
>>>> new file mode 100644
>>>> index 0000000..7d2a645
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/bus/ti-gpmc.txt
>>>> @@ -0,0 +1,77 @@
>>>> +Device tree bindings for OMAP general purpose memory controllers (GPMC)
>>>> +
>>>> +The actual devices are instantiated from the child nodes of a GPMC node.
>>>> +
>>>> +Required properties:
>>>> +
>>>> + - compatible:		Should be set to "ti,gpmc"
>>>
>>> Please, be specific. Use something like "ti,am3340-gpmc" or
>>> "ti,omap3430-gpmc". The compatible property is a list so that new
>>> devices can claim compatibility with old. Compatible strings that are
>>> overly generic are a pet-peave of mine.
>>
>> We aim to use the binding for omap2,3,4,5 as well as the am33xx devices
>> (which are omap based). Would it be sufficient to have "ti,omap2-gpmc"
>> implying all omap2+ based devices or should we have a compatible string
>> for each device supported?
> 
> Are they each register-level compatible with one another?

They are not 100% register compatible. There are a couple fields in the
binding that are only applicable to OMAP3+ devices.

> The general recommended approach here is to make subsequent silicon
> claim compatibility with the first compatible implementation.
> 
> So, for an am3358 board:
> 	compatible = "ti,am3358-gpmc", "ti,omap2420-gpmc";
> 
> Essentially, what this means is that "ti,omap2420-gpmc" is the generic
> value instead of "omap2-gpmc". The reason for this is so that the value
> is anchored against a specific implementation, and not against something
> completely imaginary or idealized. If a newer version isn't quite
> compatible with the omap2420-gpmc, then it can drop the compatible claim
> and the driver really should be told about the new device.

Ok, gotcha! I will do a register comparison and may be recommend to
Daniel which compatible strings we will need.

Thanks!
Jon