printk logbuf relocation

[Wolfgang Denk]

In message <903E17B6FF22A24C96B4E28C2C0214D7012BB481 at sr-bng-exc01.int.tsbu.net> you wrote:
>
> Hi ,
>
>   On our MPC7447+MV64360 board running Linux {both 2.4.18_mvl30 MontaVista
> PE3.0 & 2.4.20 from kernel.org} we need to carry out an experimentation.
> This  is when the board does not have any serial interface and Linux may
> hang at boot-up. The contents of printk that are logged in the log-buf are
> adequate to provide the required information. This section of memory can be
> read on next boot up. {Though this is in RAM , by turning off ECC &
> Scrubbing , we could see the contents on a reboot in the firmware which has
> a way to provide this memory dump over a PCI connection}. We could do up
> till this but the real problem starts now.
>
>   The log-buf lies in the region of memory where our firmware {a proprietary
> one } sits , so even if scrubbing is off , this overrides the logbuf
> contents. Relocating the firmware is ruled out due to other restrictions. So

We did this with U-Boot and Linux. U-Boot will pre-allocate  the  log
buffer at the very end of the RAm, and both U-Boot and Linux will use
the  same  logbuf  area.  See  the  CONFIG_LOGBUFFER  option  in  the
linux-2.4 kernel tree on our CVS server.

This  allows  to  pass  information  (hardware  diagnostics,  startup
messages)  from  the  firmware  to Linux (which will pick it up using
standard syslog tools), or to read or reset the Linux log  buffer  in
U-Boot.

If running U-Boot on your board is not an option you might be able to
copy the mechanism (if your proprietary firmware is GPL, that is).

Best regards,

Wolfgang Denk

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