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Date: Tue, 21 Apr 2020 17:19:40 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Geert Uytterhoeven <geert+renesas@...der.be>
Cc: Dmitry Osipenko <digetx@...il.com>,
Russell King <linux@...linux.org.uk>,
Nicolas Pitre <nico@...xnic.net>,
Arnd Bergmann <arnd@...db.de>,
Eric Miao <eric.miao@...dia.com>,
Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Chris Brandt <chris.brandt@...esas.com>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] ARM: boot: Obtain start of physical memory from DTB
On Wed, 15 Apr 2020 at 17:34, Geert Uytterhoeven
<geert+renesas@...der.be> 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@...xnic.net>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Reviewed-by: Nicolas Pitre <nico@...xnic.net>
> Reviewed-by: Ard Biesheuvel <ardb@...nel.org>
> Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Tested-by: Dmitry Osipenko <digetx@...il.com>
This is ready to go into the patch system, no?
The sooner Russell picks it up, the sooner I can respin my patches
that go on top.
Thanks,
> ---
> v5:
> - Add Tested-by, Reviewed-by,
> - Round up start of memory to satisfy 16 MiB alignment rule,
>
> v4:
> - Fix stack location after commit 184bf653a7a452c1 ("ARM:
> decompressor: factor out routine to obtain the inflated image
> size"),
>
> v3:
> - Add Reviewed-by,
> - Fix ATAGs with appended DTB,
> - Add Tested-by,
>
> v2:
> - Use "cmp r0, #-1", instead of "cmn r0, #1",
> - Add missing stack setup,
> - Support appended DTB.
> ---
> arch/arm/boot/compressed/Makefile | 6 ++-
> arch/arm/boot/compressed/fdt_get_mem_start.c | 57 ++++++++++++++++++++
> arch/arm/boot/compressed/head.S | 54 ++++++++++++++++++-
> 3 files changed, 115 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 9c11e7490292f0e0..82e4cee97cb5d905 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 \
> @@ -115,6 +118,7 @@ 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) $(DISABLE_ARM_SSP_PER_TASK_PLUGIN)
> 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..e29caa4cbfecb36a
> --- /dev/null
> +++ b/arch/arm/boot/compressed/fdt_get_mem_start.c
> @@ -0,0 +1,57 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include <linux/kernel.h>
> +#include <linux/sizes.h>
> +
> +#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)
> +{
> + uint32_t addr_size, mem_start;
> + const __be32 *memory;
> +
> + 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);
> +
> + mem_start = fdt32_to_cpu(memory[addr_size - 1]);
> + /* Must be a multiple of 16 MiB for phys/virt patching */
> + return round_up(mem_start, SZ_16M);
> +}
> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> index cabdd8f4a2482e2b..2d2a42865b3974da 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -254,8 +254,58 @@ 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, #24] @ 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
> +
> + /* preserve 64-bit alignment */
> + add r5, r5, #7
> + bic r5, r5, #7
> + add sp, sp, r5 @ if so, move stack above DTB
> + mov r0, r6 @ and extract memory start from DTB
> + b 2f
> +
> +1:
> +#endif /* CONFIG_ARM_APPENDED_DTB */
> +
> + mov r0, r8
> +2:
> + 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.
> @@ -273,6 +323,8 @@ not_angel:
> */
> mov r4, pc
> and r4, r4, #0xf8000000
> +
> +1:
> /* Determine final kernel image address. */
> add r4, r4, #TEXT_OFFSET
> #else
> --
> 2.17.1
>
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