[OpenWrt-Devel] [PATCH 0/3] ipq806x: add NAND flash support

Imre Kaloz kaloz at openwrt.org
Sat Aug 8 05:12:04 EDT 2015

On Fri, 07 Aug 2015 20:09:14 +0200, Felix Fietkau <nbd at openwrt.org> wrote:

> On 2015-08-07 18:50, Mathieu Olivari wrote:
>> Actually, I was asking myself the same questions yesterday. I was  
>> leaning
>> towards dts for the reasons you mention below as well; the problem is  
>> on ref
>> designs, there is no "standard" layout. The flash layout changes with  
>> time
>> (an AP148 with an old boot binary blob will have a different layout  
>> than the
>> same AP148 with a new boot image), sometimes with a certain application
>> (some boots will have an SMEM with 2 kernels & 2 rootfs for dual
>> partitioning). For this reason, and on ref designs, it'd be easier to  
>> have
>> one dts and the kernel adapting at run-time, than multiplying the dts  
>> files
>> and having to pick the right one based on your current SMEM content.

Well, there's no reason to try to support old versions or nonstandard  
designs upstream. You just have to pick the one you consider upstream  
version. For what you are looking for, you might want to take a look at  
device tree overlays.

>> I would agree that it's the exception though; on most retail routers,  
>> you
>> would have one SMEM per SKU, i.e. one layout per dts.
>> I'm thinking the most flexible way would probably to have the  
>> opportunity in
>> dts to select between "dynamic" smem partitioning, or regular "fixed"
>> partitioning. Not sure if something like this has ever been done in the
>> past; but we could explore it.
> The bcm53xx target in OpenWrt works like that. The mtd driver specifies
> two partition parsers, first ofpart, then a custom one.
> If ofpart fails to find any partitions, the custom one gets to specify
> the layout. We could probably make use of something like that for ipq as
> well.

Agreed, but I'm afraid 3rd party vendors will miss-use that as usual.

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