Thanks again for your reply to my queries.
I did not know that arch/ppc/boot stuff and u-boot were mutually
exclusive. Thanks for clarifying that.
In fact I have not been considering what is left out when you make a
uImage as opposed to zImage, obviously I have som styding to do here.
I do not understand all the intricacies of what happens regarding hardware
configuration during the eraly stages of booting linux, but I conclude
that when making a uImage one have to modify u-boot and the kernel if one
want to relocate the usage of dpram1 by the cpm uart driver. This might
have been obvious to most of you, but I was lost on this issue.
A mystery is why Dan Malek said it was a "very bad idea" to relocate the
smc buffer descriptors to anohter part of dpram1.
Maybe I will understand that one day too.
Thanks again for your help Mark.
-- Morten
"Mark Chambers" <markc at mail.com>
17.11.2004 17:37
To: <morten.banzon at axxessit.no>
cc:
Subject: Re: MPC82xx -- DPRAM1
Well, but the arch/ppc/boot stuff and u-boot are mutually exclusive,
right?
The arch/ppc/boot takes the kernel binary and wraps it in a very simple
bootloader. So it depends on your make options whether that code gets
compiled or not. So I think you've solved the mystery, that indeed the
bootloader sets up the SMCs to use that dpram memory. I guess the
philosophical question is, should it be left that way or not.
Mark Chambers
>
> >> No I still do not get this.
> >>
> >> The constant PROFF_SMC1_BASE is as far as I can see never used, only
> >> defined. Hence, the cpm or the smc will never be told by the kernel
> >> that
> >> there are pointers to the buffer descriptor tables located at
> >> PROFF_SMC1
> >> (offset zero) and PROFF_SMC2 (offset 64). Either I am blind or the
> >> kernel
> >> performs magic if this happens.
>
> >Look in arch/ppc/boot/simple/m8260_tty.c
>
> >This code, from what I can tell, is called early in boot to set up the
> >boot console. I haven't read the file very carefully, but I suspect,
> >from what Dan Malek said, that this file sets up the CPM to point the
> >SMCs at that area of dpram.
>
> Thanks for your reply.
>
> I have seen the code you are refering to. After compiling the kernel
> the arch/ppc/boot/simple directory contain no object files at all.
> Hence, I assumed that none of these files were compiled.
> To be asolutely sure I have removed the whole directory, and things
> work just fine. Which I take as a proof that nothing in the simple
> directory is involved in the configuration of smc1 as a console uart.
>
> I believe that there are only two file involved in configuring the
> cpm uart on a mpc82xx platform, namely:
> drivers/serial/cpm_uart/cpm_uart_cpm2.c
> drivers/serial/cpm_uart/cpm_uart_core.c
>
> None of these files modify the offset addresses 0x87FC (smc1) and
> 0x88FC(smc2) in the dpram2. Well, at least as far as I can tell.
> Hence, I believe the only reason why the cpm_uart driver in the kernel
> works, is because the u-boot bootloader does such a fine job.
>
> This might be intentional, I do not know but are seeking
> enlightenment.
>
> -- Morten
>
>
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