On Mon, 2013-08-26 at 20:29 +0200, Martin Hinner wrote:

On Mon, Aug 26, 2013 at 7:14 PM, Scott Wood [off-list ref] wrote:

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that kernel must be at location 0. Another problem was that interrupts
got re-enabled during execution of my bootloader (I am doing some
syscalls -> goes  to Cisco rom),

Do you mean you're calling into the rom after Linux has already started
executing?  That's not normal for 8xx.

No, in bootloader. I have disabled interrupts and then later did a
syscall which probably enabled them again. As I have overwritten some
of Cisco ROM data it crashed (at random place).

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I am also curious why CONFIG_PPC_EARLY_DEBUG_CPM uses
CONFIG_PPC_EARLY_DEBUG_CPM_ADDR as pointer to transmit SMC buffer and
not address of CPM/SCM parameter RAM ? TX buffer address can be read
from SMC parameter RAM. Wouldn't this solution be more portable? At
least this way I do it when I take over console from Cisco
startup/rommon.

The point was to keep things as simple as possible (e.g. for use in
temporary handcoded asm as needed).  This is a hacky debugging feature
that assumes you know what you're doing and can set the address to match
what the loader does (and that the loader's choice of address is
static).  If you have an improvement that keeps it simple, feel free to
send a patch.

How about making CONFIG_PPC_EARLY_DEBUG_CPM_PARRAM

PARAM

that woud carry address of SMCx parameter RAM (IMMR+0x04180 on MPC866) and this value
would be used in case CONFIG_PPC_EARLY_DEBUG_CPM_ADDR is zero ? This
would allow kernel hackers to still use
CONFIG_PPC_EARLY_DEBUG_CPM_ADDR for assembly debugging (+legacy use)
and everyone else can use it as a more reliable option that does not
rely on particular bootloader behavior. Early debug is good even for
end-users so as they can send debug output if anything goes wrong at
early stage.

If it only works with CPM1 SMC, then that should be in the name of the
symbol.

Anyway, difference between _PARRAM and _ADDR is only one lwz
instruction, so I guess it is possible to completely discard _ADDR if
there is no legacy use for it. I am also not sure if this works with
SCC UART ports or only CPM SMC UART.

Given that testing can be a challenge on this old hardware (I don't have
easy access anymore, except maybe one 8xx board), I'd rather leave the
existing mechanism in place if you don't have the ability to test all
these cases.  The ability to not care about what type of CPM serial port
it is, is an important simplification.

-Scott