[U-Boot-Users] [PATCH] add OpenGear CM4008 board support

Wolfgang Denk
2005-05-24T11:15:07Z

Dear Greg,

in message <429300A9.9050202@moreton.com.au> you wrote:
>
> > I understand this problem., It results from an unadept choice of your
> > image layout - put the kernel first, and the problems just go away
> > :-)
>
> I geuss I disagree. We see a different problem. I see u-boot doesn't
> support an established image format. You see that it does (well I think
> that is what you are saying?).

Please don't call your proprietary solution an "established image
format". It is not, and never has been, at least not in the U-Boot
context. U-Boot uses multifile images for such a purpose. Please
don't blame me if you ignored the existing solutions and came up with
somthing different which causes problems (no working boot support).

> I don't want to neccessarily turn this into a discussion about the
> merits of the format. I want this to be a discussion about how to go
> about best supporting it.

Me too.

> The size of the header is not important.

OK. Then what exactly prevents you from using a multifile image with
header?

> > It does work. I use it all the time. You just have to use tftp twice
> > - once for the filesystem and a second time for the kernel :-)
>
> Hmm, ok, you didn't say that earlier. Seems like an awful
> kludge to have to load it twice - don't you think?

I don't load anything twice - I load two separate images: one with
the kernel, and one with the file system. I always found this to be
much more flexible as you can change one component while leaving the
other in place - this is MUCH easier to debug as you change one part
of the system only, while keeping all the rest of the system (which
is probably known to be working) unchanged.

I understand that you don't want to have separate images. OK, this is
your decision. In this case U-Boot uses multifile images.

> This isn't about reading documentation. And I suspect this method
> predates u-boot anyway. When you say standard you really mean
> u-boots own methods don't you? Does any other boot loader support

U-Boot, ARMBoot, PPCBoot, Linux in general. Just emember how Linux
wraps a kernel image and an initial ramdisk image into one loadable
file.

> the same format headers? (I actually don't know the answer to
> this, thus I am genuinely asking the question).

Not with exactly the same header format. But the idea was not
completely new when I implemented it.

> For one, u-boot has no mechanism for generating arm boot tags for
> anything other than its own defined kernel format.

Right. This is intentional.

My intention my be wrong, or too limited, in which case I will be
happy to discuss beter solutions. But for your application I don't
see the need to change anything.

> > Don't use "a pretty large installed base" as an argument - it doesn't
> > count. You could have discussed your design here on the mailing list
> > BEFORE implementing your own proprietary stuff.
>
> That makes no sense, I want to use u-boot with an existing format.

What exactly is your problem with using a different format which is
supported by U-Boot?

> How can I take a multi-part image, and in Linux do
>
> erase /dev/mtd1
> cat imagefile > /dev/mtd1
> mount /dev/mtdblock1 /mnt
>
> If there is any header then that is not directly mountable as
> a filesystem.

Create _THREE_ partitions in flash: one representing the area used
for the Linux kernel (plus image headers), a second one for the root
file system, and a third one which covers both areas.

For example:

Partition Offset Size Usage
/dev/mtd0 0 256 kB U-Boot
/dev/mtd1 256 kB 768 kB Linux Kernel (with header(s))
/dev/mtd2 1024 kB 3072 kB Root Filesystem
/dev/mtd3 256 kB 3840 kB Combined Image

Then run:

erase /dev/mtd3
cat imagefile >/dev/mtd3
mount /dev/mtd2 /mnt

> You would need additional tool support to do this, and this
> either goes in Linux or u-boot.

No. I don't need any new tools.

> Sorry, just don't agree. Unadept design. It works very well
> for its intended purpose. Just not with u-boot as it is.

It does not work with U-Boot because it does not adhere to the
U-Boot's design principles. One needs to be changed. I would be
unwise to try to support the plethora of proprietary image formats in
U-Boot. Instead, we try to provide interfaces that allow to get (at
least) the same functionality. You can use these features, or ignore
them.

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
A supercomputer is a machine that runs an endless loop in 2 seconds.