[U-Boot] Some thoughts on SPL

[Simon Glass]

Hi Wolfgang,

On Sat, Dec 17, 2011 at 12:08 PM, Wolfgang Denk <wd at denx.de> wrote:
> Dear Simon Glass,
>
> In message <CAPnjgZ0E4RfzzL2tfff=CN0xQ5OV+v-QTQNy3s3zb6hn7svV2g at mail.gmail.com> you wrote:
>>
>> On Fri, Dec 16, 2011 at 9:20 AM, jonsmirl at gmail.com <jonsmirl at gmail.com> wr=
>> ote:
> ...
>> > The concept is to remove SPL as a special class and turn it into the
>> > base layer that everything builds on. Changing the model in this was
>> > should make the config files easier to understand. Instead of having a
>> > single file combining SPL and full u-boot you'd have two independent
>> > ones. In my case I'd build one u-boot config that fits into 96K and
>> > another full 250K one. Of course the two config files could each
>> > include a common base config.
> ...
>> That's one way to do it, and makes more and more sense as the amount
>> of available SRAM increases. Of course some SOCs can even set up their
>> SDRAM and read entire programs in, so there are no restrictions. But
>> for those with limitations, it makes sense to me to make SPL more a
>> cut down build of U-Boot than a special program that pulls in #ifdefed
>> code from various places.
>>
>> Another approach is to just have one U-Boot, but keep everything you
>> need to get started in the first 96KB.
>
> Please keep in mind that there is also a large number of boards that
> boot form some boot ROM (like NOR flash), i. e. that can directly
> execute _all_ U-Boot code, without need of any SPL at all.
>
> Any changes to the design of the SPL must not have any adverse
> effects on such XIP booting systems.

This is a degenerate case for the system I describe - where all the
code is in the first part and the second part is empty. It adds
nothing but for the extra build complexity already mentioned. I'm not
involved enough in SPL yet to be able to say how useful all this is,
perhaps later.

Regards,
Simon

>
> Best regards,
>
> Wolfgang Denk
>
> --
> DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
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