[U-Boot-Users] linux doesn't boot when CS for initial cache disabled

[Thomas Schäfer]

Here is what I did:

I'm testing with an IBM Walnut board (PPC405GP) with u-boot 0.3.0 and 2.4.17
kernel from Montavista. After booting u-boot and loading the kernel via
tftp, I submit the following commands on the console:

=> setdcr 12
0012: 00000004 ? 7
0012: 00000007 ? .
=> setdcr 13
0013: 400da000 ? 0
0013: 00000000 ? .

This disables CS7, which is used for the temporary stack in my
configuration.

The kernel function start_here (arch/ppc/kernel/head_4xx.S) is the place
where the MMU is used first. Setting a breakpoint (in my case at 0xc00022d0)
and trying to trace from this point with my BDI2000 results in a data
machine check interrupt:

BDI>bi 0xc00022d0
Breakpoint identification is 0
BDI>go
- TARGET: target has entered debug mode
BDI>info
    Target state      : debug mode
    Debug entry cause : instruction breakpoint
    Current PC        : 0xc00022d0
    Current CR        : 0x24004004
    Current MSR       : 0x00001030
    Current LR        : 0x0000001c
BDI>ti
    Target state      : debug mode
    Debug entry cause : JTAG stop request
    Current PC        : 0x00000280
    Current CR        : 0x28004004
    Current MSR       : 0x00000000
    Current LR        : 0xc0002b34
# Step timeout detected
BDI>

Unfortunately I have no idea why this happens. Looking at the register
contents I found that the address of the temporary stack (0x40000000) is
still stored in r2, but this should have no effect on booting the kernel???

BDI>rd
GPR00: c00022d0 07f9f5e8 40000000 c10003c0
GPR04: c0000000 00000000 007ffc00 007ffc0e
GPR08: 07fc9f10 000186a0 00000003 00000002
GPR12: 00000000 c01605b0 07fe5800 00000000
GPR16: 00000001 007ffc0e 007ffc00 ffffffff
GPR20: 00000000 07fe2398 07f9fe88 00000002
GPR24: 00000000 00000000 007ffb90 007ffc0e
GPR28: 007ffc00 00000000 00000000 007ffb90
CR   : 24004004     MSR: 00001030
BDI>

Any ideas?

Best regards,

Thomas Schaefer

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