Re: [PATCH v2] ARM: boot: Obtain start of physical memory from DTB

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Hi Geert,

On 27.01.2020 15:07, Geert Uytterhoeven wrote:
> Currently, the start address of physical memory is obtained by masking
> the program counter with a fixed mask of 0xf8000000.  This mask value
> was chosen as a balance between the requirements of different platforms.
> However, this does require that the start address of physical memory is
> a multiple of 128 MiB, precluding booting Linux on platforms where this
> requirement is not fulfilled.
>
> Fix this limitation by obtaining the start address from the DTB instead,
> if available (either explicitly passed, or appended to the kernel).
> Fall back to the traditional method when needed.
>
> This allows to boot Linux on r7s9210/rza2mevb using the 64 MiB of SDRAM
> on the RZA2MEVB sub board, which is located at 0x0C000000 (CS3 space),
> i.e. not at a multiple of 128 MiB.
>
> Suggested-by: Nicolas Pitre <nico@xxxxxxxxxxx>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> Reviewed-by: Nicolas Pitre <nico@xxxxxxxxxxx>
> ---
> Against arm/for-next.

This patch landed recently in linux-next. It breaks legacy booting from 
the zImage + appended DT + cmdline/memory info provided via ATAGs. I 
will debug it further once I find some spare time. What I noticed so 
far, the cmdline/memory info is not read from the ATAGs, only the values 
provided via appended DT are used.

> Tested with the following configurations:
>    - zImage + DTB (r8a7791/koelsch),
>    - uImage + DTB (r8a73a4/ape6evm, r7s72100/rskrza1, r7s9210/rza2mevb),
>    - zImage with appended DTB (r8a7740/armadillo, sh73a0/kzm9g).
>
> v2:
>    - Use "cmp r0, #-1", instead of "cmn r0, #1",
>    - Add missing stack setup,
>    - Support appended DTBs.
>
> v1: https://lore.kernel.org/linux-arm-kernel/20200121192741.20597-1-geert+renesas@xxxxxxxxx/
> ---
>   arch/arm/boot/compressed/Makefile            |  6 ++-
>   arch/arm/boot/compressed/fdt_get_mem_start.c | 52 ++++++++++++++++++++
>   arch/arm/boot/compressed/head.S              | 52 +++++++++++++++++++-
>   3 files changed, 108 insertions(+), 2 deletions(-)
>   create mode 100644 arch/arm/boot/compressed/fdt_get_mem_start.c
>
> diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> index da599c3a11934332..bbfecd648a1a3b57 100644
> --- a/arch/arm/boot/compressed/Makefile
> +++ b/arch/arm/boot/compressed/Makefile
> @@ -86,12 +86,15 @@ libfdt_objs	:= $(addsuffix .o, $(basename $(libfdt)))
>   $(addprefix $(obj)/,$(libfdt) $(libfdt_hdrs)): $(obj)/%: $(srctree)/scripts/dtc/libfdt/%
>   	$(call cmd,shipped)
>   
> -$(addprefix $(obj)/,$(libfdt_objs) atags_to_fdt.o): \
> +$(addprefix $(obj)/,$(libfdt_objs) atags_to_fdt.o fdt_get_mem_start.o): \
>   	$(addprefix $(obj)/,$(libfdt_hdrs))
>   
>   ifeq ($(CONFIG_ARM_ATAG_DTB_COMPAT),y)
>   OBJS	+= $(libfdt_objs) atags_to_fdt.o
>   endif
> +ifeq ($(CONFIG_USE_OF),y)
> +OBJS	+= $(libfdt_objs) fdt_get_mem_start.o
> +endif
>   
>   targets       := vmlinux vmlinux.lds piggy_data piggy.o \
>   		 lib1funcs.o ashldi3.o bswapsdi2.o \
> @@ -116,6 +119,7 @@ CFLAGS_fdt.o := $(nossp-flags-y)
>   CFLAGS_fdt_ro.o := $(nossp-flags-y)
>   CFLAGS_fdt_rw.o := $(nossp-flags-y)
>   CFLAGS_fdt_wip.o := $(nossp-flags-y)
> +CFLAGS_fdt_get_mem_start.o := $(nossp-flags-y)
>   
>   ccflags-y := -fpic $(call cc-option,-mno-single-pic-base,) -fno-builtin -I$(obj)
>   asflags-y := -DZIMAGE
> diff --git a/arch/arm/boot/compressed/fdt_get_mem_start.c b/arch/arm/boot/compressed/fdt_get_mem_start.c
> new file mode 100644
> index 0000000000000000..2c5ac47f656317ee
> --- /dev/null
> +++ b/arch/arm/boot/compressed/fdt_get_mem_start.c
> @@ -0,0 +1,52 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include <libfdt.h>
> +
> +static const void *getprop(const void *fdt, const char *node_path,
> +			   const char *property)
> +{
> +	int offset = fdt_path_offset(fdt, node_path);
> +
> +	if (offset == -FDT_ERR_NOTFOUND)
> +		return NULL;
> +
> +	return fdt_getprop(fdt, offset, property, NULL);
> +}
> +
> +static uint32_t get_addr_size(const void *fdt)
> +{
> +	const __be32 *addr_len = getprop(fdt, "/", "#address-cells");
> +
> +	if (!addr_len) {
> +		/* default */
> +		return 1;
> +	}
> +
> +	return fdt32_to_cpu(*addr_len);
> +}
> +
> +/*
> + * Get the start of physical memory
> + */
> +
> +unsigned long fdt_get_mem_start(const void *fdt)
> +{
> +	const __be32 *memory;
> +	uint32_t addr_size;
> +
> +	if (!fdt)
> +		return -1;
> +
> +	if (*(__be32 *)fdt != cpu_to_fdt32(FDT_MAGIC))
> +		return -1;
> +
> +	/* Find the first memory node */
> +	memory = getprop(fdt, "/memory", "reg");
> +	if (!memory)
> +		return -1;
> +
> +	/* There may be multiple cells on LPAE platforms */
> +	addr_size = get_addr_size(fdt);
> +
> +	return fdt32_to_cpu(memory[addr_size - 1]);
> +}
> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> index 927f5dc413d7dff2..aa2d7de2ddc86fa8 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -235,8 +235,56 @@ not_angel:
>   		.text
>   
>   #ifdef CONFIG_AUTO_ZRELADDR
> +#ifdef CONFIG_USE_OF
>   		/*
> -		 * Find the start of physical memory.  As we are executing
> +		 * Find the start of physical memory.
> +		 * Try the DTB first, if available.
> +		 */
> +		adr	r0, LC0
> +		ldr	r1, [r0]	@ get absolute LC0
> +		ldr	sp, [r0, #28]	@ get stack location
> +		sub	r1, r0, r1	@ compute relocation offset
> +		add	sp, sp, r1	@ apply relocation
> +
> +#ifdef CONFIG_ARM_APPENDED_DTB
> +		/*
> +		 * Look for an appended DTB. If found, use it and
> +		 * move stack away from it.
> +		 */
> +		ldr	r6, [r0, #12]	@ get &_edata
> +		add	r6, r6, r1	@ relocate it
> +		ldmia	r6, {r0, r5}	@ get DTB signature and size
> +#ifndef __ARMEB__
> +		ldr	r1, =0xedfe0dd0	@ sig is 0xd00dfeed big endian
> +		/* convert DTB size to little endian */
> +		eor	r2, r5, r5, ror #16
> +		bic	r2, r2, #0x00ff0000
> +		mov	r5, r5, ror #8
> +		eor	r5, r5, r2, lsr #8
> +#else
> +		ldr	r1, =0xd00dfeed
> +#endif
> +		cmp	r0, r1		@ do we have a DTB there?
> +		bne	1f
> +
> +		mov	r8, r6		@ use it if so
> +		/* preserve 64-bit alignment */
> +		add	r5, r5, #7
> +		bic	r5, r5, #7
> +		add	sp, sp, r5	@ and move stack above it
> +
> +1:
> +#endif /* CONFIG_ARM_APPENDED_DTB */
> +
> +		mov	r0, r8
> +		bl	fdt_get_mem_start
> +		mov	r4, r0
> +		cmp	r0, #-1
> +		bne	1f
> +#endif /* CONFIG_USE_OF */
> +
> +		/*
> +		 * Fall back to the traditional method.  As we are executing
>   		 * without the MMU on, we are in the physical address space.
>   		 * We just need to get rid of any offset by aligning the
>   		 * address.
> @@ -254,6 +302,8 @@ not_angel:
>   		 */
>   		mov	r4, pc
>   		and	r4, r4, #0xf8000000
> +
> +1:
>   		/* Determine final kernel image address. */
>   		add	r4, r4, #TEXT_OFFSET
>   #else

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland




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