[U-Boot] [PATCH 1/2 V3] arm926: Flush the data cache before disabling it

[Albert ARIBAUD <albert.u.boot@aribaud.net>]

Hi Sughosh,

Le 14/01/2012 08:49, Sughosh Ganu a ?crit :
> The current implementation invalidates the cache instead of flushing
> it. This causes problems on platforms where the spl/u-boot is already
> loaded to the RAM, with caches enabled by a first stage bootloader.
>
> The V bit of the cp15's control register c1 is set to the value of
> VINITHI on reset. Do not clear this bit by default, as there are SOC's
> with no valid memory region at 0x0.
>
> Also fix the comments to match code.
>
> Signed-off-by: Sughosh Ganu<urwithsughosh@gmail.com>
> ---
>
> Changes since V2
> * Added code to invalidate I cache, based on review comment by Aneesh.
> * Fixed comments to match the code.
>
> Changes since V1
> * Added arm926 keyword to the subject line
> * Removed the superfluous setting of r0.
> * Fixed the comment to reflect the fact that V is not being cleared
>
>   arch/arm/cpu/arm926ejs/start.S |   14 +++++++++-----
>   1 files changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm/cpu/arm926ejs/start.S b/arch/arm/cpu/arm926ejs/start.S
> index 6a09c02..91a9325 100644
> --- a/arch/arm/cpu/arm926ejs/start.S
> +++ b/arch/arm/cpu/arm926ejs/start.S
> @@ -355,17 +355,21 @@ _dynsym_start_ofs:
>    */
>   cpu_init_crit:
>   	/*
> -	 * flush v4 I/D caches
> +	 * flush D cache before disabling it
>   	 */
>   	mov	r0, #0
> -	mcr	p15, 0, r0, c7, c7, 0	/* flush v3/v4 cache */
> -	mcr	p15, 0, r0, c8, c7, 0	/* flush v4 TLB */
> +flush_dcache:
> +	mrc	p15, 0, r15, c7, c10, 3
> +	bne	flush_dcache
> +
> +	mcr	p15, 0, r0, c8, c7, 0	/* invalidate TLB */
> +	mcr	p15, 0, r0, c7, c5, 0	/* invalidate I Cache */
>
>   	/*
> -	 * disable MMU stuff and caches
> +	 * disable MMU and D cache, and enable I cache.
>   	 */
>   	mrc	p15, 0, r0, c1, c0, 0
> -	bic	r0, r0, #0x00002300	/* clear bits 13, 9:8 (--V- --RS) */
> +	bic	r0, r0, #0x00000300	/* clear bits 9:8 ( --RS) */

NAK--this alters the functioning of U-Boot for many boards in ways 
unpredictable. If you want to get this specific V change into ARM, then 
please also add code to set V in all relevant SoCs, or (better yet IMO) 
make "do not set V in cpu_init_crit" a config option and set it in the 
relevant SoCs or boards.

>   	bic	r0, r0, #0x00000087	/* clear bits 7, 2:0 (B--- -CAM) */
>   	orr	r0, r0, #0x00000002	/* set bit 2 (A) Align */
>   	orr	r0, r0, #0x00001000	/* set bit 12 (I) I-Cache */

Amicalement,
-- 
Albert.