[U-Boot] [PATCH 1/2] armv8: Support loading 32-bit OS in AArch32 execution state

[Alexander Graf <agraf@suse.de>]

On 13.05.16 10:40, Alison Wang wrote:
> To support loading a 32-bit OS, the execution state will change from
> AArch64 to AArch32 when jumping to kernel.
> 
> The architecture information will be got through checking FIT
> image, then U-Boot will load 32-bit OS or 64-bit OS automatically.
> 
> Signed-off-by: Ebony Zhu <ebony.zhu@nxp.com>
> Signed-off-by: Alison Wang <alison.wang@nxp.com>
> Signed-off-by: Chenhui Zhao <chenhui.zhao@nxp.com>
> ---
>  arch/arm/cpu/armv8/transition.S | 100 ++++++++++++++++++++++++++++++++++++++++
>  arch/arm/include/asm/system.h   |   2 +
>  arch/arm/lib/bootm.c            |  20 +++++++-
>  common/image-fit.c              |  12 ++++-
>  4 files changed, 131 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/cpu/armv8/transition.S b/arch/arm/cpu/armv8/transition.S
> index 253a39b..9d7a17a 100644
> --- a/arch/arm/cpu/armv8/transition.S
> +++ b/arch/arm/cpu/armv8/transition.S
> @@ -21,3 +21,103 @@ ENTRY(armv8_switch_to_el1)
>  0:	ret
>  1:	armv8_switch_to_el1_m x0, x1
>  ENDPROC(armv8_switch_to_el1)
> +
> +/*
> + * x0: kernel entry point
> + * x1: machine nr
> + * x2: fdt address
> + */
> +ENTRY(armv8_switch_to_el2_aarch32)
> +	switch_el x3, 1f, 0f, 0f
> +0:	ret
> +1:
> +	mov	x7, x0
> +	mov	x8, x1
> +	mov	x9, x2
> +
> +	/* 32bit EL2 | HCE | SMD | RES1 (Bits[5:4]) | Non-secure EL0/EL1 */
> +	mov	x1, 0x1b1
> +	msr	scr_el3, x1
> +	msr	cptr_el3, xzr	/* Disable coprocessor traps to EL3 */
> +	mov	x1, 0x33ff
> +	msr	cptr_el2, x1	/* Disable coprocessor traps to EL2 */
> +
> +	/* Initialize Generic Timers */
> +	msr	cntvoff_el2, xzr
> +
> +	mov	x1, #0x0830
> +	movk	x1, #0x30c5, lsl #16
> +	msr	sctlr_el2, x1

Why is this necessary?

> +
> +	/* Return to AArch32 Hypervisor mode */
> +	mov	x1, sp
> +	msr	sp_el2, x1
> +	mrs	x1, vbar_el3
> +	msr	vbar_el2, x1	/* Migrate VBAR */
> +	mov	x1, #0x1da
> +	msr	spsr_el3, x1
> +	msr	elr_el3, x7
> +
> +	mov	x0, #0
> +	mov	x1, x8
> +	mov	x2, x9
> +
> +	eret
> +ENDPROC(armv8_switch_to_el2_aarch32)

This whole thing looks like a copy of armv8_switch_to_el2_m. Just
parameterize that one and put the few bits that are different in macro ifs.

> +
> +/*
> + * x0: kernel entry point
> + * x1: machine nr
> + * x2: fdt address
> + */
> +ENTRY(armv8_switch_to_el1_aarch32)
> +	switch_el x3, 0f, 1f, 0f
> +0:	ret
> +1:
> +	mov	x7, x0
> +	mov	x8, x1
> +	mov	x9, x2
> +
> +	/* Initialize Generic Timers */
> +	mrs	x0, cnthctl_el2
> +	orr	x0, x0, #0x3		/* Enable EL1 access to timers */
> +	msr	cnthctl_el2, x0
> +	msr	cntvoff_el2, xzr
> +
> +        /* Initialize MPID/MPIDR registers */
> +	mrs	x0, midr_el1
> +	mrs	x1, mpidr_el1
> +	msr	vpidr_el2, x0
> +	msr	vmpidr_el2, x1
> +
> +        /* Disable coprocessor traps */
> +	mov	x0, #0x33ff
> +	msr	cptr_el2, x0		/* Disable coprocessor traps to EL2 */
> +        msr	hstr_el2, xzr		/* Disable coprocessor traps to EL2 */
> +        mov	x0, #3 << 20
> +        msr	cpacr_el1, x0		/* Enable FP/SIMD at EL1 */
> +
> +	/* Initialize HCR_EL2 */
> +	mov	x0, #(0 << 31)		/* 32bit EL1 */
> +	orr	x0, x0, #(1 << 29)	/* Disable HVC */
> +	msr	hcr_el2, x0
> +
> +	mov	x0, #0x0800
> +	movk	x0, #0x30d0, lsl #16
> +	msr	sctlr_el1, x0
> +
> +	/* Return to AArch32 Supervisor mode */
> +	mov	x0, sp
> +	msr	sp_el1, x0		/* Migrate SP */
> +	mrs	x0, vbar_el2
> +	msr	vbar_el1, x0		/* Migrate VBAR */
> +	mov     x0, #0x1d3
> +	msr	spsr_el2, x0
> +	msr	elr_el2, x7
> +
> +	mov	x0, #0
> +	mov	x1, x8
> +	mov	x2, x9
> +
> +	eret
> +ENDPROC(armv8_switch_to_el1_aarch32)

Does anybody really care about jumping to el1?

> diff --git a/arch/arm/include/asm/system.h b/arch/arm/include/asm/system.h
> index 9ae890a..bb87cf0 100644
> --- a/arch/arm/include/asm/system.h
> +++ b/arch/arm/include/asm/system.h
> @@ -102,6 +102,8 @@ void __asm_switch_ttbr(u64 new_ttbr);
>  
>  void armv8_switch_to_el2(void);
>  void armv8_switch_to_el1(void);
> +void armv8_switch_to_el2_aarch32(u64 entry_point, u64 mach_nr, u64 fdt_addr);
> +void armv8_switch_to_el1_aarch32(u64 entry_point, u64 mach_nr, u64 fdt_addr);
>  void gic_init(void);
>  void gic_send_sgi(unsigned long sgino);
>  void wait_for_wakeup(void);
> diff --git a/arch/arm/lib/bootm.c b/arch/arm/lib/bootm.c
> index 0838d89..a39c3d2 100644
> --- a/arch/arm/lib/bootm.c
> +++ b/arch/arm/lib/bootm.c
> @@ -286,8 +286,24 @@ static void boot_jump_linux(bootm_headers_t *images, int flag)
>  	announce_and_cleanup(fake);
>  
>  	if (!fake) {
> -		do_nonsec_virt_switch();
> -		kernel_entry(images->ft_addr, NULL, NULL, NULL);
> +		if ((IH_ARCH_DEFAULT == IH_ARCH_ARM64) &&
> +		    (images->os.arch == IH_ARCH_ARM)) {
> +			smp_kick_all_cpus();
> +			dcache_disable();
> +#ifdef CONFIG_ARMV8_SWITCH_TO_EL1
> +			armv8_switch_to_el2();
> +			armv8_switch_to_el1_aarch32((u64)images->ep,
> +						    (u64)gd->bd->bi_arch_number,
> +						    (u64)images->ft_addr);
> +#else
> +			armv8_switch_to_el2_aarch32((u64)images->ep,
> +						    (u64)gd->bd->bi_arch_number,
> +						    (u64)images->ft_addr);
> +#endif

Does this compile on 32bit targets?


Alex