Re: [RFC PATCH 04/11] sunxi: Add lowlevel switch to aarch64

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 11.05.23 01:37, Jules Maselbas wrote:
> Allwinner A64 SoC (and probably others) boots in 32-bits mode. Switching
> to aarch64 is achieved by writing to the Reset Management Register (RMR)
> which can be accessed through the memory space thanks to an alias.
> 
> On A64 this alias is located at 0x017000a0
> ---
>  arch/arm/include/asm/barebox.lds.h |  2 ++
>  arch/arm/mach-sunxi/Kconfig        |  5 ++++
>  arch/arm/mach-sunxi/Makefile       |  2 ++
>  arch/arm/mach-sunxi/rmr_switch.S   | 47 ++++++++++++++++++++++++++++++
>  include/mach/sunxi/barebox.lds.h   |  6 ++++
>  include/mach/sunxi/rmr_switch.h    | 10 +++++++
>  6 files changed, 72 insertions(+)
>  create mode 100644 arch/arm/mach-sunxi/rmr_switch.S
>  create mode 100644 include/mach/sunxi/barebox.lds.h
>  create mode 100644 include/mach/sunxi/rmr_switch.h
> 
> diff --git a/arch/arm/include/asm/barebox.lds.h b/arch/arm/include/asm/barebox.lds.h
> index a5c74381d8..f94290128e 100644
> --- a/arch/arm/include/asm/barebox.lds.h
> +++ b/arch/arm/include/asm/barebox.lds.h
> @@ -2,6 +2,8 @@
>  
>  #if defined CONFIG_ARCH_EP93XX
>  #include <mach/ep93xx/barebox.lds.h>
> +#elif defined CONFIG_ARCH_SUNXI
> +#include <mach/sunxi/barebox.lds.h>
>  #endif

As mentioned, we should leave it to the linker to elide the unneeded headers
instead of the preprocessor, so we enable multi-image across SoCs/SoC families.

>  
>  #ifdef CONFIG_CPU_32
> diff --git a/arch/arm/mach-sunxi/Kconfig b/arch/arm/mach-sunxi/Kconfig
> index 0e8d83fedd..e28f04c354 100644
> --- a/arch/arm/mach-sunxi/Kconfig
> +++ b/arch/arm/mach-sunxi/Kconfig
> @@ -4,6 +4,11 @@ config ARCH_TEXT_BASE
>  	hex
>  	default 0x0
>  
> +config SUNXI_RVBAR_IOMAP
> +	hex
> +	default 0x017000a0  if ARCH_SUN50I_A64
> +	# default 0x09010040 if ARCH_SUN50I_H5

Both of these are ARMv8, so there should be no reason to prevent
a build that targets both SoCs. Could you move this into a header
that defines both SUN50I_H5_RVBAR_IOMAP and
ARCH_SUN50I_A64_RVBAR_IOMAP

> +
>  menuconfig SUNXI_MULTI_BOARDS
>  	bool "Allwinner boards"
>  	select HAVE_PBL_MULTI_IMAGES
> diff --git a/arch/arm/mach-sunxi/Makefile b/arch/arm/mach-sunxi/Makefile
> index d678973ca2..e7fa23c832 100644
> --- a/arch/arm/mach-sunxi/Makefile
> +++ b/arch/arm/mach-sunxi/Makefile
> @@ -1,2 +1,4 @@
>  obj-y += sunxi.o
>  lwl-y += cpu_init.o
> +
> +pbl-$(CONFIG_CPU_64) += rmr_switch.o
> diff --git a/arch/arm/mach-sunxi/rmr_switch.S b/arch/arm/mach-sunxi/rmr_switch.S
> new file mode 100644
> index 0000000000..bfe3b75e3a
> --- /dev/null
> +++ b/arch/arm/mach-sunxi/rmr_switch.S
> @@ -0,0 +1,47 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +/*
> + * ARMv8 RMR reset sequence on Allwinner SoCs.
> + *
> + * All 64-bit capable Allwinner SoCs reset in AArch32 (and continue to
> + * exectute the Boot ROM in this state), so we need to switch to AArch64

execute

> + * at some point.
> + * Section G6.2.133 of the ARMv8 ARM describes the Reset Management Register
> + * (RMR), which triggers a warm-reset of a core and can request to switch
> + * into a different execution state (AArch32 or AArch64).
> + * The address at which execution starts after the reset is held in the
> + * RVBAR system register, which is architecturally read-only.
> + * Allwinner provides a writable alias of this register in MMIO space, so
> + * we can easily set the start address of AArch64 code.
> + * This code below switches to AArch64 and starts execution at the specified
> + * start address.
> + *
> + * This file has been adapted from U-Boot code sources:
> + *  - arch/arm/mach-sunxi/rmr_switch.S
> + *  - arch/arm/include/asm/arch-sunxi/boot0.h.
> + *
> + * The aarch32 assembly has already been assembled and are inserted verbatime
> + * as .word statements (the asm source is commented for each statement).
> + *
> + */
> +
> +#include <config.h>
> +#include <linux/linkage.h>
> +
> +.section .text_head_rmr_switch, "x"
> +ENTRY(sunxi_rmr_switch)		/* arm32		arm64		*/
> +	.word 0xeb000000	/* bl	.+8		subs x0, x0, x0	*/
> +	b end			/* .word 0x1400000c 	b end		*/
> +	.word 0xe59f0020	/* ldr	r0, [pc, #32] ; rvbar		*/
> +	.word 0xe580e000	/* str  lr, [r0]			*/
> +	.word 0xf57ff04f	/* dsb	sy				*/
> +	.word 0xf57ff06f	/* isb	syo				*/
> +	.word 0xee1c0f50	/* mrc	15, 0, r0, cr12, cr0, {2}	*/
> +	.word 0xe3800003	/* orr	r0, r0, #3			*/
> +	.word 0xee0c0f50	/* mcr	15, 0, r0, cr12, cr0, {2}	*/
> +	.word 0xf57ff06f	/* isb	sy				*/
> +	.word 0xe320f003	/* 1b: wfi				*/
> +	.word 0xeafffffd	/* b	1b				*/
> +	.word CONFIG_SUNXI_RVBAR_IOMAP
> +	.align 3 /* prevent linker script from adding padding for aligment */
> +end:	/* fall-through */
> +ENDPROC(sunxi_rmr_switch)
> diff --git a/include/mach/sunxi/barebox.lds.h b/include/mach/sunxi/barebox.lds.h
> new file mode 100644
> index 0000000000..e04c713611
> --- /dev/null
> +++ b/include/mach/sunxi/barebox.lds.h
> @@ -0,0 +1,6 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +/* theses two sections should only be needed for the pbl */
> +#define ENTRY_HEADER \
> +	*(.text_head_egon_header*)		\
> +	*(.text_head_rmr_switch*)


I'd rather suggest a SUNXI_ENTRY_FUNCTION(name, rvbar, x0, x1, x2) macro and then
a more specific SUN50I_A64_ENTRY_FUNCTION(name, x0, x1, x2)

> diff --git a/include/mach/sunxi/rmr_switch.h b/include/mach/sunxi/rmr_switch.h
> new file mode 100644
> index 0000000000..2ecbd81d57
> --- /dev/null
> +++ b/include/mach/sunxi/rmr_switch.h
> @@ -0,0 +1,10 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +
> +#ifndef __MACH_RMR_SWITCH_H
> +#define __MACH_RMR_SWITCH_H
> +
> +/* 64-bits Allwinner SoCs reset in AArch32 and need to switch to AArch64 */
> +extern const u32 sunxi_rmr_switch[];
> +#define	sunxi_switch_to_aarch64() __keep_symbolref(sunxi_rmr_switch)
> +
> +#endif

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