[U-Boot] [PATCH 1/3] config: introduce a generic $bootcmd

[Stephen Warren <swarren@wwwdotorg.org>]

On 08/11/2014 11:51 AM, Jeroen Hofstee wrote:
> Hello Stephan
>
> On 11-08-14 18:53, Stephen Warren wrote:
>> On 08/10/2014 10:53 AM, Jeroen Hofstee wrote:
>>> Hello Stephan,
>>>
>>> On 10-08-14 05:11, Stephen Warren wrote:
>>>> The entire point of this series is to prevent distros from having to
>>>> install bootloader-specific boot configuration files.
>> >
>>> I fail to see why this is something to pursue. Since the distro knows
>>> the boot path, why should u-boot be polling all possible options?
>>
>> This patch series allows U-Boot to find the OS and boot it. U-Boot is
>> searching for some kind of boot configuration file.
>>
>> This part of the process is the same as the BIOS searching all known
>> possible boot devices for a partition marked bootable, and with a
>> valid MBR. Or, it's the same as UEFI searching all possible boot
>> devices for whatever config file or boot binary is mandated by UEFI.
>
> Not in my mind, I am not against scanning the possible
> boot devices, on the contrary, I am trying to add booting
> the userland from usb instead of mmc for the rpi_b.

The following will tell U-Boot to only search USB for extlinux.conf.

setenv boot_targets usb

(you can put this into /uEnv.txt on the SD card if you want to avoid 
editing U-Boot source code to make this change; there's no persistent 
environment storage on the Pi, at least at the moment)

 > The
> part I dislike is where it starts searching for specific files.
> The equivalent would be your BIOS actively searching for GRUB,
> LILO, Windows Boot manager etc. etc. and as a fallback
> try the MBR.
...
>> Once U-Boot locates extlinux.conf or boot.scr, that file encodes what
>> files (kernel, DTB, initrd)
>
> This is the part I get for free now with it, I don't really like it,
> since if we take this road it ends up looking for e.g. grub.conf,
> ubldr.conf, vxworks.conf etc etc.

No, Linux distros need to be able to install a single bootloader 
configuration file to tell the bootloader how to boot. I definitely 
don't want to add support for a ton of other bootloader configuration 
file formats. There needs to be a single standard that distros know they 
can rely on.

> Also in this case the downstream provides information back,
> albeit tiny, it does indicate if it is bootable and a label to explain
> what is bootable.

I don't understand what that means.