Help ! 2.6.14 kernel can't bring up

Help ! 2.6.14 kernel can't bring up

[zjznliang]

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Re: Help ! 2.6.14 kernel can't bring up

[Clemens Koller]

Hello, zjznliang!

zjznliang wrote:
> Hi linuxppc-embedded！
> 
> 	Hi , How to config the "early printk" in 2.6.14 linux configration???

Well... check the .config or the kernel sources for
CONFIG_EARLY_PRINTK
or
CONFIG_WANT_EARLY_SERIAL

Have a look at the bootup code of your board, where it's used.
I would call the printk as soon as the serial ports are initialized.
If that's too late, try to toggle some pin as early as possible.
If that doesn't work, and if you have no more ideas of what to do,
you might think about getting some hardware debugging tools.

Best greets,
-- 
Clemens Koller
_______________________________
R&D Imaging Devices
Anagramm GmbH
Rupert-Mayer-Str. 45/1
81379 Muenchen
Germany

http://www.anagramm.de
Phone: +49-89-741518-50
Fax: +49-89-741518-19

Re: Help ! 2.6.14 kernel can't bring up

[David H. Lynch Jr.]

zjznliang wrote:
> Hi linuxppc-embedded！
>
> 	Hi , How to config the "early printk" in 2.6.14 linux configration???
>
>
>  	
Console and debugging I/O is available at all stages of The Linux
loading process - If the drivers for your board support it.
There is nearly free support for 8250 like serial ports, in virtually
all boards. Support for other debugging IO devices is fairly simple to
setup.

I used the arch/ppc/syslib/mv64x60_dbg.c and
arch/ppc/boot/simple/mv64x60_tty.c as templates to create trivial
drivers for debugging IO
on hardware that had no relation to a UART.

I think "early printk" refers to the early serial driver that can be
used after the kernel has uncompressed itself and relocated itself and
switched to
a virtual environment. For 8250 like serial ports that can enabled in
the linux .config file setup by make menuconfig or whatever variant of
make xxconfig
you prefer. For non-8250 like uarts you will again have to write an
early serial driver. All the early debug IO drivers are trivial - little
more is needed than
an implementation of putc, as opposed to the full conolse support
required for a tty on a booted system.

Re: Help ! 2.6.14 kernel can't bring up

[David H. Lynch Jr]

 I was stuck at exactly this point for over a week. Basically, at this
point lots of things happen all at once:
Prior to this the MMU has had a small collection of TLB's setup.
The 6 lines of code you listed:
change from whatever Machine Status you powered up in to the proper
Machine status for running the kernel with memory translation and
exception handling enabled.
and switch from executing using physical addresses to executing using
virtual addresses.
and "jump" via the "rfi" from real mode to virtual mode at virtual
address start_here.

If you are using a LED IO port for debugging, then you MUST setup a TLB
entry for that LED or after the rfi you will not be able to write to it.
There should be a setup tlb block inside a CONFIG_SERIAL_TEXT_DEBUG
block copy it, change the address to match your LED port and set a new
index and your LED debug port should be good to go.

In my instance, my problem turned out to be with Machine Check
exceptions - The moment that rfi executes not only is virtual memory
enabled - but all exception handling is turned on.
I was able to find this my "testing" things one bit in the MSR at a
time, until I figured out which ones could be turned on and which could not.


zjznliang wrote:
> Hello David H. Lynch Jr.,！
>
> 	Now ,I am tracing the code in Linux 2.6.14 in head_8xx.S .
> 	I used led to trace the procedure,and I found the block in it .
> 	
> 644	/* Now turn on the MMU for real! */
> 645		li	r4,MSR_KERNEL
> 646		lis	r3,start_kernel@h
> 647		ori	r3,r3,start_kernel@l
> 648		mtspr	SPRN_SRR0,r3
> 649		mtspr	SPRN_SRR1,r4
> 650		rfi			/* enable MMU and jump to start_kernel */
>
> I set the led between the 649 and 650 ,and the led was light ,
> but when I set the led in the function start_kernel the led is not
> light .
>
> I thought the function start_kernel was not jumped to .
>
> what do you think ?
>   

Help ! 2.6.14 kernel can't bring up

[zjznliang]

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Re: Help ! 2.6.14 kernel can't bring up

[Clemens Koller]

Hello, zjznliang!

zjznliang wrote:
> And there is nothing output ,I thought that it was serial port fault.
> I checked my Linux configuration ,but found nothing .

Check your kernel configuration.
Have you tried to turn on "early printk" support in your kernel config?
Linux might be booting already, but you just don't see it on your console.

Good luck,

-- 
Clemens Koller
_______________________________
R&D Imaging Devices
Anagramm GmbH
Rupert-Mayer-Str. 45/1
81379 Muenchen
Germany

http://www.anagramm.de
Phone: +49-89-741518-50
Fax: +49-89-741518-19