[OpenWrt-Devel] [PATCH 3/3] linux: add support of Synopsys ARC boards

[Jonas Gorski]

Hi,

On Thu, Sep 3, 2015 at 6:11 PM, Alexey Brodkin
<Alexey.Brodkin at synopsys.com> wrote:
> Hi Jonas,
>
> On Thu, 2015-09-03 at 15:33 +0200, Jonas Gorski wrote:
>> Hi,
>>
>> On Wed, Sep 2, 2015 at 10:40 PM, Alexey Brodkin
>> <Alexey.Brodkin at synopsys.com> wrote:
>> > Hi Jonas,
>> >
>> > On Wed, 2015-09-02 at 10:32 +0200, Jonas Gorski wrote:
>> > > Also please move
>> > > all common options from both subtargets into a
>> > > target/linux/arc/config-4.1.
>> >
>> > Well indeed there're same options in both configs.
>> > But please note nSIM and AXS10x are completely different boards.
>> > And each of those boards may have different CPU.
>> >
>> > This first set of patches only covers ARC legacy architecture (ARC 700).
>> >
>> > But with 4.2 release of Linux kernel new gen ARC architecture (ARC HS38)
>> > was introduced and once that patch set is accepted in OpenWRT I'll
>> > send another patch that add support of new gen ARC CPUs.
>> >
>> > My plan was to have following files structure:
>> >
>> > target/linux/arc/axs10x/profiles/arc700.mk
>> >                                 /archs38.mk
>> >                 /nsim/profiles/arc700.mk
>> >                               /archs38.mk
>> >
>> > Is it acceptable or I need to modify it?
>>
>> That seems backward, since arc700 and hs38 are different
>> architectures, so I would assume their kernels and toolchains won't be
>> compatible.
>>
>> So I would use
>>
>> target/linuxarc/arc700
>> and
>> target/linux/arc/hs38
>>
>> and then
>>
>> target/linux/arc/profiles/axs10x.mk
>> and
>> target/linux/arc/profiles/nsim.mk
>>
>> (You can have "toplevel" profiles that apply to all subtargets)
>
> Well I don't understand how that will work.
> I mean we need to have different:
>  [1] kernel config options for both pairs: boards (axs10x vs nsim)
>      and architectures (arcv1 vs arcv2)
>  [2] basefiles for boards (axs10x vs nsim)
>
> I.e. setting profiles for axs10x and nsim won't be enough.
>
> Maybe this all is not very clear, so I'll try to put here what we need to accommodate:
>  [1] For axs10x board:
>     a) base files for axs10x board
>     b) kernel options for axs10x board
>     c) kernel options for arc700 core in axs10x
>     d) kernel options for archs38 core in axs10x
>
>  [2] For nsim board:
>     a) base files for nsim board
>     b) kernel options for nsim board
>     c) kernel options for arc700
> core in nsim
>     d) kernel options for archs38 core in nsim
>
> So maybe the only option that will work is having 2 top-level arc entries like:
>  * target/linux/arcv1 (or arc700)
>  * target/linux/arcv2 (or archs38)
>
> Or another alternative is 4 subtargets like that (I see something similar for RPi,
> see target/linux/brcm2708):

brcm2708 does this because bcm2709 supports a newer arm instruction
set, so to not be limited by the older one we split it into 2708 and
2709. If they both supported the same arm version, then there would be
no need for subtargets.

>  * target/linux/axs101 (which is axs10x with arc700)
>  * target/linux/axs103 (which is axs10x with archs38)
>  * target/linux/nsim_700 (which is nsim with arc700)
>  * target/linux/nsim_hs (which is nsim with archs38)
>
> But that in its turn will require to duplicate basefiles and kernel configs
> relevant to boards but not cores.
>
> Any thoughts about that are much appreciated.

Unfortunately that is not how OpenWrt is supposed to work. The
expectation is that a (sub)target is for all boards that share a
certain (family of) SoCs, not just a single board. Looking at Linux
4.2, you are using device tree, so I would assume it would be possible
to build a kenrel that "supports" all boards with a arc700 cpu,
through passing the appropriate dtb to it. And likewise for the hs38.
If the bootloader does not support passing a dtb, then it maybe
appending a dtb like on ARM would be an option; or reserving  space in
the kernel to patch in a dtb (we have a patch for MIPS for that, but
that would likely work similar for other targets).

Having a subtarget for each board will create a huge burden for
release builds, es effectively we will then need to build a new
toolchain for each board, and they cannot share their packages feeds,
so we would also need to rebuild all packages for all boards.

So please rework your target to not use/require per-board subtargets.


Jonas
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