Re: [PATCH] sunxi: Load sun8i secure monitor to SRAM A2

[Andre Przywara <andre.przywara@arm.com>]

On Sun, 18 Apr 2021 22:21:41 -0500
Samuel Holland <samuel@sholland.org> wrote:

Hi Samuel,

> Most sun6i-derived SoCs contain SRAM A2, a secure SRAM area for ARISC
> SCP firmware. H3 has a smaller SRAM than other SoCs (A31/A33/A23/A83T).
> 
> On sun8i SoCs which do not have SRAM B, we can use part of this SRAM for
> the secure monitor. Follow the design of 64-bit SoCs and use the first
> part for the monitor, and the last 16 KiB for the SCP firmware. With
> this change, the monitor no longer needs to reserve a region in DRAM.

So this commit message reads a bit more innocent than the patch is, can
you amend this? It took me a while to see what it really does ...

For a start, I'd suggest to rename the subject to "Move secure
monitor...".
And it's good to explain where we come from (SRAM B vs. SRAM A2), but I
would like to see an explicit list of SoCs that get changed, because
all those different sun8i.h, cpu_sun4i.h and CONFIG_SUN8I parts are
super confusing to the casual reader.

Maybe something along the lines of:
So far for the H3, A23, and A33 SoCs, we use DRAM to hold the secure
monitor. And while those SoCs do not have the secure SRAM B like older
SoCs, there is enough (secure) SRAM A2 to put the monitor code and data
in there instead ....

Regardless of that, the patch is nice, I always disliked reserving a
small piece of DRAM somewhere in the middle of it.
If I see this correctly, this just leaves the R40 using DRAM for the
secure monitor (with V3s and A83T not using PSCI)?

Cheers,
Andre

> 
> Signed-off-by: Samuel Holland <samuel@sholland.org>
> ---
>  arch/arm/include/asm/arch-sunxi/cpu_sun4i.h | 11 +++++++++++
>  include/configs/sun8i.h                     |  7 +++++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/arch/arm/include/asm/arch-sunxi/cpu_sun4i.h b/arch/arm/include/asm/arch-sunxi/cpu_sun4i.h
> index 02ce73954d..d4c795d89c 100644
> --- a/arch/arm/include/asm/arch-sunxi/cpu_sun4i.h
> +++ b/arch/arm/include/asm/arch-sunxi/cpu_sun4i.h
> @@ -11,7 +11,18 @@
>  #define SUNXI_SRAM_A1_BASE		0x00000000
>  #define SUNXI_SRAM_A1_SIZE		(16 * 1024)	/* 16 kiB */
>  
> +#if defined(CONFIG_SUNXI_GEN_SUN6I) && \
> +    !defined(CONFIG_MACH_SUN8I_R40) && \
> +    !defined(CONFIG_MACH_SUN8I_V3S)
> +#define SUNXI_SRAM_A2_BASE		0x00040000
> +#ifdef CONFIG_MACH_SUN8I_H3
> +#define SUNXI_SRAM_A2_SIZE		(48 * 1024)	/* 16+32 kiB */
> +#else
> +#define SUNXI_SRAM_A2_SIZE		(80 * 1024)	/* 16+64 kiB */
> +#endif
> +#else
>  #define SUNXI_SRAM_A2_BASE		0x00004000	/* 16 kiB */
> +#endif
>  #define SUNXI_SRAM_A3_BASE		0x00008000	/* 13 kiB */
>  #define SUNXI_SRAM_A4_BASE		0x0000b400	/* 3 kiB */
>  #define SUNXI_SRAM_D_BASE		0x00010000	/* 4 kiB */
> diff --git a/include/configs/sun8i.h b/include/configs/sun8i.h
> index 9b4675e4c3..545d27996c 100644
> --- a/include/configs/sun8i.h
> +++ b/include/configs/sun8i.h
> @@ -12,6 +12,13 @@
>   * A23 specific configuration
>   */
>  
> +/*
> + * Skip the first 16 KiB of SRAM A2, which is not usable, as only certain bytes
> + * are writable. Reserve the last 17 KiB for the resume shim and SCP firmware.
> + */
> +#define CONFIG_ARMV7_SECURE_BASE	(SUNXI_SRAM_A2_BASE + 16 * 1024)
> +#define CONFIG_ARMV7_SECURE_MAX_SIZE	(SUNXI_SRAM_A2_SIZE - 33 * 1024)
> +
>  /*
>   * Include common sunxi configuration where most the settings are
>   */