[U-Boot-Users] Safe firmware updates

[Wolfgang Denk]

In message <9D8FC3304AA0924E9CD0A211DFEDCBAB0164D90A at bespin.apdcomms.co.uk> you wrote:
> 
> >There is no need to change anything. U-Boot is perfectly  capable  of
> >supporting such requirements.
> 
> That's great news, but how?

For example, use a hush shell script.

> >Why would you do that if the new image is already in flash? 
> 
> I considered of doing it like this because we have limited flash space
> and need to re-use a flash partition normally usually for logging data.
> We haven't got enough space to store 2 copies of the uImage, and 2

But the procvedure you described sounded like storing two versions of
the image, and if you're looking for *SAFE* updates you have no other
choice anyway (except for  providing  an  emergency  boot  mode  from
external storage (USB stick, CF card, etc.) or over the network.

> copies of the cramfs file system. We could automatically change the
> mtdparts parameter in bootargs after each update to reflect this, but
> this would mean a change to u-boot and its getting too complicated
> again.

Why do you think that changing bootargs  (or  any  other  environment
variable)  means  "a change to u-boot"? It's just a variable setting,
which can be changed any time, no matter if running U-Boot or Linux.

> I understand I could put a second bootm command in bootargs to
> automatically switch boot address, but how would I swap cramfs file
> systems in a safe way? The flash partition used for the cramfs is
> currently specified using 'root=/dev/mtdblock2' in bootargs, but I
> don't
> see how to make u-boot change this to say 'root=/dev/mtdblock3
> automatically'.

Where exactly is the problem? There are *many* ways  to  solve  this;
for example, you can start with definitios like these:

	setenv kernel_addr 0xDEADBEEF
	setenv rootpart 2
	setenv setroot 'setenv bootargs root=/dev/mtdblock${rootpart}'
	setenv add_foo 'setenv bootargs ${bootargs} foo'
	setenv add_bar 'setenv bootargs ${bootargs} bar'
	...
	setenv bootcmd 'run setroot add_foo add_bar ... ; bootm ${kernel_addr}'

Then all you need to do is change the "kernel_addr" variable to  boot
using  a different kernel image; and change "rootpart" to boot from a
different partition. Alternatively, you could as  well  redefine  the
MTD partition map using the mtdargs mechanism, etc. etc.

See http://www.denx.de/wiki/view/DULG/LinuxBootArgs


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Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
There's an old proverb that says just about whatever you want it to.