linux-kernel - Re: [RFC PATCH 00/16] OMAP: GPMC: Restructure OMAP GPMC driver (NAND) : DT binding change proposal

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Message-ID: <537F03C8.3070101@ti.com>
Date:	Fri, 23 May 2014 11:16:08 +0300
From:	Roger Quadros <rogerq@...com>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Tony Lindgren <tony@...mide.com>,
	Javier Martinez Canillas <javier@...hile0.org>
CC:	Brian Norris <computersforpeace@...il.com>,
	"Gupta, Pekon" <pekon@...com>,
	Robert Nelson <robertcnelson@...il.com>,
	Jingoo Han <jg1.han@...sung.com>, <dwmw2@...radead.org>,
	<nsekhar@...com>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	<linux-mtd@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>
Subject: Re: [RFC PATCH 00/16] OMAP: GPMC: Restructure OMAP GPMC driver (NAND)
 : DT binding change proposal

Ezequiel & Javier,

On 05/22/2014 05:46 PM, Ezequiel Garcia wrote:
> On 22 May 01:51 PM, Javier Martinez Canillas wrote:
>> On Thu, May 22, 2014 at 10:12 AM, Roger Quadros <rogerq@...com> wrote:
>>>> On 21 May 02:20 PM, Roger Quadros wrote:
>>>>>
>>>>> For DT boot:
>>>>> - The GPMC controller node should have a chip select (CS) node for each used
>>>>>   chip select. The CS node must have a child device node for each device
>>>>>   attached to that chip select. Properties for that child are GPMC agnostic.
>>>>>
>>>>>   i.e.
>>>>>      gpmc {
>>>>>              cs0 {
>>>>>                      nand0 {
>>>>>                      }
>>>>>              };
>>>>>
>>>>>              cs1 {
>>>>>                      nor0 {
>>>>>                      }
>>>>>              }
>>>>>              ...
>>>>>      };
>>>>>
>>>>
>>>> While I agree that the GPMC driver is a bit messy, I'm not sure it's possible
>>>> to go through such a complete devicetree binding re-design (breaking backwards
>>>> compatibility) now that the binding is already in production.
>>>
>>> Why not? especially if the existing bindings are poorly dones. Is anyone using these
>>> bindings burning the DT into ROM and can't change it when they update the kernel?
>>>
>>
>> While I do agree that your DT bindings are much better than the
>> current ones, there is a policy that DT bindings are an external API
>> and once are released with a kernel are set in stone and can't be
>> changed.
>>
> 
> Exactly. The DT binding is considered an ABI. Thus, invariant across kernel
> versions. Users can't be coherced into a DTB update after a kernel update.
> 
> That said, I don't really care if you break compatilibity in this case.
> Rather, I'm suggesting that you make sure this change is going to be accepted
> upstream, before doing any more work. The DT maintainers are reluctant to do
> so.

Appreciate your concern.

Would be really nice if you can review patches 1-12. They have nothing to do with DT changes.
Thanks.

cheers,
-roger

> 
> On the other side, I guess you will also break bisectability while breaking
> backward compatibility. Doesn't sound very nice.
> 

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