[U-Boot] [PATCH 1/2] sunxi: Downclock AHB1 to 100MHz on Allwinner A64

[Siarhei Siamashka <siarhei.siamashka@gmail.com>]

On Tue, 31 May 2016 01:48:05 +0300
Siarhei Siamashka <siarhei.siamashka@gmail.com> wrote:

> Currently the AHB1 clock speed is configured as 200MHz by
> the SPL, but this causes a subtle and hard to reproduce data
> corruption in SRAM C (for example, this can't be easily
> detected with a trivial memset/memcmp test).
> 
> For what it's worth, the Allwinner's BSP configures AHB1
> as 200MHz, as can be verified by running the devmem2 tool
> in the system running the Allwinner's kernel 3.10.x:
> 
>    0x1C20028: PLL_PERIPH0_CTRL_REG = 0x90041811
>    0x1C20054: AHB1_APB1_CFG_REG    = 0x3180
>    0x1C20058: APB2_CFG_REG         = 0x1000000
>    0x1C2005C: AHB2_CFG_REG         = 0x1
> 
> However the FEL mode uses more conservative settings (100MHz
> for AHB1):
> 
>    0x1C20028: PLL_PERIPH0_CTRL_REG = 0x90041811
>    0x1C20054: AHB1_APB1_CFG_REG    = 0x3180

Oops, a copy-paste issue when editing the commit message, this
should be 0x3190

>    0x1C20058: APB2_CFG_REG         = 0x1000000
>    0x1C2005C: AHB2_CFG_REG         = 0x0
> 
> It is yet to be confirmed whether faster AHB1/AHB2 clock settings
> can be used safely if we initialize the AXP803 PMIC instead of
> using reset defaults. But in order to resolve the data corruption
> problem right now, it's best to downclock AHB1 to a safe level.
> 
> Note that this issue only affects the SPL, which is not fully
> supported on Allwinner A64 yet and it should not affect the boot0
> usage (unless somebody can confirm SRAM C corruption with the
> boot0 too).
> 
> Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
> ---
>  arch/arm/include/asm/arch-sunxi/clock_sun6i.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm/include/asm/arch-sunxi/clock_sun6i.h b/arch/arm/include/asm/arch-sunxi/clock_sun6i.h
> index f2990db..c2e72f5 100644
> --- a/arch/arm/include/asm/arch-sunxi/clock_sun6i.h
> +++ b/arch/arm/include/asm/arch-sunxi/clock_sun6i.h
> @@ -222,7 +222,12 @@ struct sunxi_ccm_reg {
>  #define CCM_PLL11_CTRL_UPD		(0x1 << 30)
>  #define CCM_PLL11_CTRL_EN		(0x1 << 31)
>  
> +#if defined(CONFIG_MACH_SUN50I)
> +/* AHB1=100MHz failsafe setup from the FEL mode, usable with PMIC defaults */
> +#define AHB1_ABP1_DIV_DEFAULT		0x00003190 /* AHB1=PLL6/6,APB1=AHB1/2 */
> +#else
>  #define AHB1_ABP1_DIV_DEFAULT		0x00003180 /* AHB1=PLL6/3,APB1=AHB1/2 */
> +#endif
>  
>  #define AXI_GATE_OFFSET_DRAM		0

-- 
Best regards,
Siarhei Siamashka