[U-Boot] [patch/rfc] rm9200 lowevel_init: don't touch reserved/readonly registers

[David Brownell <david-b@pacbell.net>]

On Tuesday 09 June 2009, David Brownell wrote:
> For some reason the AT91rm9200 lowlevel init writes to a bunch of
> reserved or read-only addresses.  All the boards seem to define the
> value-to-be-written values as zero ... but they shouldn't actually
> be writing *anything* there.

Repeat:  should not write to reserved or read-ony addresses.


> If there's a real need to write these locations, like an erratum
> that's not included in the current list, that should be reflected
> in a source code comment.  Looks like maybe some very early BDI-2000
> setup code has been carried along by cargo cult programming since
> at least late 2004 (per GIT history).
> 
> Meanwhile, here's a patch/RFC disabling what seems to be bogosity.
> If it's eventually a "go", the supporting code should be removed.

No comments?



> ---
>  cpu/arm920t/at91rm9200/lowlevel_init.S |   10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> --- a/cpu/arm920t/at91rm9200/lowlevel_init.S
> +++ b/cpu/arm920t/at91rm9200/lowlevel_init.S
> @@ -81,6 +81,7 @@ LoopOsc:
>  	bne	0b
>  	/* delay - this is all done by guess */
>  	ldr	r0, =0x00010000
> +	/* (vs reading PMC_SR for LOCKA, LOCKB ... or MOSCS earlier) */
>  1:
>  	subs	r0, r0, #1
>  	bhi	1b
> @@ -108,16 +109,22 @@ LoopOsc:
>  	.ltorg
>  
>  SMRDATA:
> +#if 0
> +/* MC_PU* are reserved "do not use" memory controller addresses;
> + * see table 16-1 of the rm9200 manual
> + */
>  	.word AT91C_MC_PUIA
>  	.word CONFIG_SYS_MC_PUIA_VAL
>  	.word AT91C_MC_PUP
>  	.word CONFIG_SYS_MC_PUP_VAL
>  	.word AT91C_MC_PUER
>  	.word CONFIG_SYS_MC_PUER_VAL
> +/* MC_ASR/AASR are read-only registers, see table 16-1 again */
>  	.word AT91C_MC_ASR
>  	.word CONFIG_SYS_MC_ASR_VAL
>  	.word AT91C_MC_AASR
>  	.word CONFIG_SYS_MC_AASR_VAL
> +#endif
>  	.word AT91C_EBI_CFGR
>  	.word CONFIG_SYS_EBI_CFGR_VAL
>  	.word AT91C_SMC_CSR0
> @@ -128,8 +135,7 @@ SMRDATA:
>  	.word CONFIG_SYS_PLLBR_VAL
>  	.word AT91C_MCKR
>  	.word CONFIG_SYS_MCKR_VAL
> -	/* SMRDATA is 80 bytes long */
> -	/* here there's a delay of 100 */
> +	/* here there's a delay */
>  SMRDATA1:
>  	.word AT91C_PIOC_ASR
>  	.word CONFIG_SYS_PIOC_ASR_VAL
>