[U-Boot] [PATCH 3/4] config_distro_bootcmd: Scan all partitions for boot files

[Ian Campbell]

On Wed, 2015-01-07 at 11:10 +0100, Sjoerd Simons wrote:
> On Tue, 2015-01-06 at 17:43 -0700, Stephen Warren wrote:
> > (CCing Dennis so he can comment from a distro perspective re: partition 
> > table bootable flags v.s. scanning all partitions)
> > 
> > On 01/06/2015 10:07 AM, Sjoerd Simons wrote:
> > > On Mon, 2015-01-05 at 13:24 -0700, Stephen Warren wrote:
> > >> On 01/05/2015 10:13 AM, Sjoerd Simons wrote:
> 
> > > Well my thoughts on the matter are above, If folks feel strongly about
> > > this approach being the wrong way I'd love to hear their arguments :).
> > 
> > One issue with this approach is that there's no way for the user to 
> > short-circuit the scanning. If I put a ChromiumOS install on an SD card 
> > and leave it plugged into a system that's going to end up booting from 
> > eMMC since that's where the boot files are, there are lots of partitions 
> > to scan on that SD card, which will be a bit annoying.
> 
> 
> I don't remember exactly how many partitions with fat/ext* filesystems a
> ChromiumOS installation has (order of 3-5 iirc?), but indeed it means
> your boot will be a bit slower due to it probing more partitions.
> Wouldn't expect it to significantly slow down the total boot time
> though.

I thought u-boot would scan that partitions which were marked bootable
first, in which case you just need to set the bit correctly in the
partition table. I might be wrong about that though. (and re-reading
$subject, it seems like changing this is the subject of the thread...)

> I didn't think of this one my WIP is on an Odroid X2 which has a boot
> selector jumper, so I have it always starting from mmc0 (which is either
> SD or EMMC depending on the jumper setting). 
> 
> However, it raises an interesting question. The current convention for
> Exynos is to first scans external storage (SD, mmc 1) and then internal
> storage (eMMC, mmc 0), which opens up a whole different can of worms. As
> that means that e.g. my chromebook will try to boot from whatever random
> SD i've put into it first rather the OS installed on eMMC.  It would be
> nice to have some general guidelines in this area so the behaviour of
> various boards can be somewhat consistent in the default behaviour.

My understanding was that the various ${boot_*} envvars, including
boot_targets, are considered to be user serviceable parts. IOW if you
want to boot from mmc0 only then:
        setenv boot_targets mmc0
        saveenv

Maybe it makes sense for the default boot order to differ depending on
the specific exynos platform though?

Ian.

> (Added Ian Cambell to the cc as he introduce the usage on exynos
> devices)
>