[U-Boot] Uboot and memory test

[Wolfgang Denk]

Dear markus74 at bredband.net,

In message <d7989a847972829bac8c26247783ce71 at imap.bredband.net> you wrote:
>
> This is a question related to memory testing from within Uboot:

Actually this is not quite correct. Your question is a very general
one and only artially related to U-Boot, if at all.

> On a CPU (ppc476) there is 2 GB RAM which is tested in Uboot (the
> operating system uses this memory). On the same CPU there is an
> additional 256 MB memory chip which is used only by the IP-stack and not
> the operating system. 

You are talking about some out-of-tree port, so we do not know either
the actual code you are referring to nor the design criteria that were
applied when creating this port - it is therefor impossible for us to
know what U-Boot is doing on your board.

Even if a certain RAM area is reserved for specal purposes in some OS
this does not necessarily mean that this is true also for U-Boot.

> The question is, should this 256 MB memory be
> tested from Uboot or should the IP-stack test this memory? 

It depends on your specific requirements whether you test the memory
at all, how thoroughly you test it (just using the basic test in
get_ram_size() or the mtest variants or the full POST test code?),
when and how often you test it (at boot, at shut down, at specific
command? Only sometimes or always?), and which memory regions you
include into the test.

There are literally hundrets of systems in mainline wehre U-Boot does
not perform any memory tests at all.

The only clear answer I have for you is that it is certain that the IP
stack shall NOT perform any memory tests.  This is not what it was
designed for.  Well, yes, you can use a microscope as a hammer, but
such use is strongly discouraged.

Best regards,

Wolfgang Denk

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