[U-Boot-Users] u-boot and Linux kernel forward compatibility is unsure?

[U-Boot-Users] u-boot and Linux kernel forward compatibility is unsure?

[Leon Woestenberg]

Hello all,

triggered by the e-mail below (which solved my issue, thanks Kim) I
have the following question:

For how long can I expect current u-boot (say 1.3.4) to be forward
compatible with newer Linux kernels?

It seems the u-boot from only half a year old cannot boot a current
Linux kernel (!).

I typically work on products where the initial boot loader is adapted
to provide fail-safe upgrades and itself is never upgraded to prevent
the chance of non-flashable (bricked) products in the very small
chance something goes wrong during the boot loader update.

How do people deal with using u-boot in a fail-safe environment where
the chance of brickage must be zero and the (initial) bootloader
itself cannot be updated?
Should I plan for a second stage loader?

Also, is there any plan to add fail-safe features to u-boot?

Regards,

Leon.

On Wed, May 28, 2008 at 9:38 PM, Kim Phillips
<kim.phillips@freescale.com> wrote:
> On Wed, 28 May 2008 21:33:33 +0200
> "Leon Woestenberg" <leon.woestenberg@gmail.com> wrote:
>
>> I have tried to run the vanilla upstream 2.6.25.4 kernel on my
>> U-Boot 1.3.0-rc2 (Nov 19 2007 - 16:37:36) MPC83XX
>>
>> Is this u-boot too old, i.e. might there be a compatibility issue
> yes
> start by updating u-boot
>

Regards,
-- 
Leon

[U-Boot-Users] u-boot and Linux kernel forward compatibility is unsure?

[Wolfgang Denk]

Dear Leon,

in message <c384c5ea0805281514r1740072fw7c49101a4535f818@mail.gmail.com> you wrote:
> 
> triggered by the e-mail below (which solved my issue, thanks Kim) I
> have the following question:
> 
> For how long can I expect current u-boot (say 1.3.4) to be forward
> compatible with newer Linux kernels?

I think chances are pretty good. Please keep in mind that we're right
in the middle of a really big change - the merging  of  the  arch/ppc
and arch/ppc64 code into a common arch/powerpc tree is something that
hits  many  areas  pretty  heavily, and the device tree support which
many things depend upon is still a (fast) moving target.

But even today you can build a current Linux kernel using the cuImage
wrapper and boot it on an old (say, version 1.2.0) U-Boot.


Please do not confuse compatibility with "having all the latest and
greatest new interfaces as well". 

I think you have to get used to the thought that the Linux kernel  is
undergoing serious changes right now (which means you cannot consider
it  stable  enough to use the latest version in a project where long-
term compatibility is an issue).

> It seems the u-boot from only half a year old cannot boot a current
> Linux kernel (!).

Only if you try to use the latest features. Use  a  cuImage,  and  it
should just work fine.

> I typically work on products where the initial boot loader is adapted
> to provide fail-safe upgrades and itself is never upgraded to prevent
> the chance of non-flashable (bricked) products in the very small
> chance something goes wrong during the boot loader update.

Been there, too.

> How do people deal with using u-boot in a fail-safe environment where
> the chance of brickage must be zero and the (initial) bootloader
> itself cannot be updated?

You will probably have to accept that software updates are restricted
to certain versions. If you started with a  root  file  system  build
around  a  2.4  Linux  kernel,  you  will probably have problems when
trying to use a current 2.6 kernel with this  file  system  image  as
well.  There  may  (or  may  not)  be  compatibility layers (like the
cuImage wrapper) that extend that period, but there is no guarantee.

> Should I plan for a second stage loader?

You already have one - Linux. Use kexec if you really think you must.

> Also, is there any plan to add fail-safe features to u-boot?

What are you thinking of?

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
"Wagner's music is better than it sounds."               - Mark Twain

[U-Boot-Users] u-boot and Linux kernel forward compatibility is unsure?

[Leon Woestenberg]

Hello Wolfgang,

On Thu, May 29, 2008 at 12:41 AM, Wolfgang Denk <wd@denx.de> wrote:
> in message <c384c5ea0805281514r1740072fw7c49101a4535f818@mail.gmail.com> you wrote:
>>
>> For how long can I expect current u-boot (say 1.3.4) to be forward
>> compatible with newer Linux kernels?
>
> I think chances are pretty good. Please keep in mind that we're right
>
> But even today you can build a current Linux kernel using the cuImage
> wrapper and boot it on an old (say, version 1.2.0) U-Boot.
>
Thanks for your clear answer, takes away my cloud of doubt.

>> Also, is there any plan to add fail-safe features to u-boot?
>
> What are you thinking of?
>
My main requirement is to have the bootloader make a decision to boot
a fall back image in case the normal image does not boot (for whatever
reason). The fall back image is a user friendly way to unbrick the
device. It itself is never overwritten. (In my case a web server with
firmware upgrade Java applet, for example).

Currently, my flow is as follows (with implementation in redboot)

boot loader:
enable hardware watchdog
if flag A is set
  clear flag A
  load normal image, boot
  else if the normal image was not loaded, boot fallback.
else
  boot fallback

the normal image sets flag A when it wants to reboot, then stops
servicing the watchdog and resets

if normal image either did not set flag A (it crashes) or it did not
service the watchdog, the watchdog will reset the board.

I wonder if this is a common use and if it makes sense to implement
this for mainstream u-boot, or is this very specific?

Regards,
-- 
Leon

[U-Boot-Users] u-boot and Linux kernel forward compatibility is unsure?

[Wolfgang Denk]

In message <c384c5ea0805291600v28d281d2o2b65068a0cb88651@mail.gmail.com> you wrote:
> 
> I wonder if this is a common use and if it makes sense to implement
> this for mainstream u-boot, or is this very specific?

This is common use, and U-Boot already support it. See the bootcount
feature (http://www.denx.de/wiki/view/DULG/UBootBootCountLimit), and
read about alternative images in the new image format
(doc/uImage.FIT/*).

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
They're usually so busy thinking about what  happens  next  that  the
only  time they ever find out what is happening now is when they come
to look back on it.                 - Terry Pratchett, _Wyrd Sisters_