Subject: Re: [PATCH] PowerPC: Remove hardcoded BAT configuration of IMMR in CPM early debug console

From: Scott Wood <[email-masked]>
Date: Fri, 28 May 2010 11:18:57 -0500

On 05/28/2010 10:18 AM, Martyn Welch wrote:
> The CPM early debug console hardcodes the BAT to cover the IMMR at
> 0xf0000000. The IMMR (on the mpc8270 at the very least) can be set to a
> number of locations with bootstrap configuration, which are outside the
> hardcoded BAT configuration.
>
> This patch determines the correct location at which to configure a BAT
> during the boot process from the supplied PPC_EARLY_DEBUG_CPM_ADDR.
>
> Signed-off-by: Martyn Welch<[email-masked]>
> ---
>
>   arch/powerpc/kernel/head_32.S    |    5 +++--
>   arch/powerpc/sysdev/cpm_common.c |    4 +++-
>   2 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
> index e025e89..861cace 100644
> --- a/arch/powerpc/kernel/head_32.S
> +++ b/arch/powerpc/kernel/head_32.S
> @@ -1194,12 +1194,13 @@ setup_disp_bat:
>   #endif /* CONFIG_BOOTX_TEXT */
>
>   #ifdef CONFIG_PPC_EARLY_DEBUG_CPM
> +#define PPC_EARLY_DEBUG_CPM_ADDR ASM_CONST(CONFIG_PPC_EARLY_DEBUG_CPM_ADDR)
>   setup_cpm_bat:
> -	lis	r8, 0xf000
> +	lis	r8, PPC_EARLY_DEBUG_CPM_ADDR@ha
>   	ori	r8, r8,	0x002a
>   	mtspr	SPRN_DBAT1L, r8
>
> -	lis	r11, 0xf000
> +	lis	r11, PPC_EARLY_DEBUG_CPM_ADDR@ha
>   	ori	r11, r11, (BL_1M << 2) | 2
>   	mtspr	SPRN_DBAT1U, r11

Only the physical address should depend on where IMMR is.  We should use 
fixmap instead of an arbitrary address for the effective address. 
There's a existing FIX_EARLY_DEBUG_BASE, but it's only 128 KiB so we'll 
have to either grow it, or map only a subset of IMMR.

Plus, CONFIG_PPC_EARLY_DEBUG_CPM_ADDR points to the TX descriptor, not 
to the beginning of IMMR, so you should mask off the lower 20 bits (the 
offset is probably less than 64K, and the BAT might just ignore the 
extra bits anyway, but why take chances?).

-Scott