[Buildroot] [PATCH 1/4] configs: at91sam9x5ek: add development rootfs

[Ludovic Desroches]

On Fri, Nov 04, 2016 at 02:53:49PM +0100, Thomas Petazzoni wrote:
> Hello,
> 
> On Fri, 4 Nov 2016 14:14:08 +0100, Ludovic Desroches wrote:
> 
> > > That's a lot of configurations for a single board. Can we rationalize a
> > > bit, and chose one configuration only (either NAND or MMC), for which
> > > we have the minimal and dev configurations?
> > 
> > I have in mind, but maybe I am wrong since the conversion is not recent,
> > you told me having several defconfigs for the same board  won't be an issue.
> > The concern was more about having a dev_defconfig.
> 
> Well, the issue is the overall multiplication of defconfigs, so both
> the fact that you have separate defconfigs for MMC and NAND, and the
> fact that you want to have those "dev_defconfig" contribute to the
> multiplication of defconfigs.
> 
> > Without a defconfig targetted to NAND or MMC, the customer will have to
> > recompile the at91bootstrap and u-boot, this is something we would like
> > to avoid. I think u-boot case could be handled because the difference is
> > mainly about environment variables. Concerning at91bootstrap, it is more
> > complex. If you have any suggestion to handle this case and so reducing
> > the number of defconfig variants, I would be happy.
> 
> Is it possible to have a single at91bootstrap for both the NAND and MMC
> scenarios? I guess you can decide depending on the boot source whether
> you should load u-boot from NAND or from MMC. However, this means you
> need to have both the NAND code and MMC code compiled in the same
> at91bootstrap image. Maybe this makes the at91bootstrap image too big?
> I'm not sure what are the constraints of the ROM code in terms of first
> stage bootloader size on this SoC.

No, it is not possible to get a single at91bootstrap to manage several
boot medias. The boot media selection is an exclusive choice. Removing
this constraint rises two potential issues:
- the size, we may have a binary too big as you said for some SoCs (only
  24KB)
- we need to decide at execution time the boot media but we have no
  guarantee that all components are on the same media.


Ludovic