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

[Jeroen Hofstee <jeroen@myspectrum.nl>]

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
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.

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.

> U-Boot performs this searching before having any knowledge of the OS; 
> there's no way for the OS to parameterize this search path, just like 
> OSs don't configure a PC BIOS to search a specific HDD/floppy/CDROM 
> for the MBR to boot.
>

Yup as said, this is the part I was looking for.

> 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.

I will have a look if I can tame the script, without modifying it nor
u-boot, but I guess that is not possible since boot.scr comes after
extlinux not before.

Regards,
Jeroen