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

[Stephen Warren <swarren@wwwdotorg.org>]

On 01/07/2015 03:10 AM, 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.

IIRC something more like 12-16, at least for the developer builds I have 
used in the past.

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

The user can select which devices get looked at by setting $boot_targets 
to a list of devices names, e.g. "mmc1 mmc0 usb pxe".