On Fri, Jun 17, 2016 at 09:51:49PM +0900, Masahiro Yamada wrote:
> There are two enable methods supported by ARM64 Linux; psci and
> spin-table. The latter is simpler and easier to use for quick SoC
> bring-up.
>
> So, I used the spin-table for my first ARMv8 SoC porting, but I
> found its support in U-Boot was poor. It is true there exists a
> code fragment for the spin code in arch/arm/cpu/armv8/start.S,
> but I see some problems:
>
> - We must hard-code CPU_RELEASE_ADDR so that it matches the
> "cpu-release-addr" property in the DT that comes from the
> kernel tree.
>
> - The Documentation/arm64/booting.txt in Linux requires that
> the release address must be zero-initialized, but it is not
> cared by the common code in U-Boot. So, we must do it in a
> board specific manner.
>
> - There is no systematic way to protect the spin code from the
> kernel. U-Boot relocates itself during the boot, so it is
> difficult to predict where the spin code will be located
> after the relocation, which makes it even more difficult to
> hard-code /memreserve/ in the DT of the kernel. One possible
> work-around would be to pre-fetch the spin-code into the
> I-cache of secondary CPUs, but this is an unsafe solution.
>
> So, here is a patch to solve the problems. In this approach, the DT
> is run-time modified to reserve the spin code (+ cpu-release-addr).
> Also, the "cpu-release-addr" property is set to an appropriate
> address after the relocation, which means we no longer need the
> hard-coded CPU_RELEASE_ADDR.
>
> Currently this patch only supports ARMv8, but theoretically nothing
> about the spin-table is arch-specific. Perhaps, we might want to
> support it on PowerPC in the future. So, I put the DT fixup code
> into the common/ directory. Very little code must be written in
> assembler, which went to the arch/arm/cpu/armv8/ directory.
It's worth noting that while both arm64 and PPC have something called
"spin-table", they're not quite the same. The arm64 version just reused
the enable-method and property names for something different (and
arch-specific).
I have no strong feelings about where the code lives, however.
Otherwise, these sound like useful improvements.
Thanks,
Mark.
>
> Signed-off-by: Masahiro Yamada <yamada.masah...@socionext.com>
> ---
>
> arch/arm/cpu/armv8/Kconfig | 18 +++++++++++
> arch/arm/cpu/armv8/Makefile | 1 +
> arch/arm/cpu/armv8/spin_table_v8.S | 22 ++++++++++++++
> arch/arm/cpu/armv8/start.S | 10 +++---
> arch/arm/lib/bootm-fdt.c | 7 +++++
> common/Makefile | 1 +
> common/spin_table.c | 62
> ++++++++++++++++++++++++++++++++++++++
> include/spin_table.h | 14 +++++++++
> 8 files changed, 131 insertions(+), 4 deletions(-)
> create mode 100644 arch/arm/cpu/armv8/spin_table_v8.S
> create mode 100644 common/spin_table.c
> create mode 100644 include/spin_table.h
>
> diff --git a/arch/arm/cpu/armv8/Kconfig b/arch/arm/cpu/armv8/Kconfig
> index 3d19bbf..019b625 100644
> --- a/arch/arm/cpu/armv8/Kconfig
> +++ b/arch/arm/cpu/armv8/Kconfig
> @@ -3,4 +3,22 @@ if ARM64
> config ARMV8_MULTIENTRY
> boolean "Enable multiple CPUs to enter into U-Boot"
>
> +config SPIN_TABLE
> + bool "Support spin-table enable method"
> + depends on ARMV8_MULTIENTRY && OF_LIBFDT
> + help
> + Say Y here to support "spin-table" enable method for booting Linux.
> +
> + To use this feature, you must do:
> + - Specify enable-method = "spin-table" in each CPU node in the
> + Device Tree you are using to boot the kernel
> + - Let secondary CPUs in U-Boot (in a board specific manner)
> + before the master CPU jumps to the kernel
> +
> + U-Boot automatically does:
> + - Set "cpu-release-addr" property of each CPU node
> + (overwrites it if already exists).
> + - Reserve the code for the spin-table and the release address
> + via a /memreserve/ region in the Device Tree.
> +
> endif
> diff --git a/arch/arm/cpu/armv8/Makefile b/arch/arm/cpu/armv8/Makefile
> index 1c85aa9..2e3f421 100644
> --- a/arch/arm/cpu/armv8/Makefile
> +++ b/arch/arm/cpu/armv8/Makefile
> @@ -15,6 +15,7 @@ obj-y += cache.o
> obj-y += tlb.o
> obj-y += transition.o
> obj-y += fwcall.o
> +obj-$(CONFIG_SPIN_TABLE) += spin_table_v8.o
>
> obj-$(CONFIG_FSL_LAYERSCAPE) += fsl-layerscape/
> obj-$(CONFIG_ARCH_ZYNQMP) += zynqmp/
> diff --git a/arch/arm/cpu/armv8/spin_table_v8.S
> b/arch/arm/cpu/armv8/spin_table_v8.S
> new file mode 100644
> index 0000000..2f1bd61
> --- /dev/null
> +++ b/arch/arm/cpu/armv8/spin_table_v8.S
> @@ -0,0 +1,22 @@
> +/*
> + * Copyright (C) 2016 Masahiro Yamada <yamada.masah...@socionext.com>
> + *
> + * SPDX-License-Identifier: GPL-2.0+
> + */
> +
> +#include <linux/linkage.h>
> +
> +ENTRY(spin_table_secondary_jump)
> +.globl spin_table_reserve_begin
> +spin_table_reserve_begin:
> +0: wfe
> + ldr x0, spin_table_cpu_release_addr
> + cbz x0, 0b
> + br x0
> +.globl spin_table_cpu_release_addr
> + .align 3
> +spin_table_cpu_release_addr:
> + .quad 0
> +.globl spin_table_reserve_end
> +spin_table_reserve_end:
> +ENDPROC(spin_table_secondary_jump)
> diff --git a/arch/arm/cpu/armv8/start.S b/arch/arm/cpu/armv8/start.S
> index 670e323..15ca864 100644
> --- a/arch/arm/cpu/armv8/start.S
> +++ b/arch/arm/cpu/armv8/start.S
> @@ -94,7 +94,11 @@ reset:
> /* Processor specific initialization */
> bl lowlevel_init
>
> -#ifdef CONFIG_ARMV8_MULTIENTRY
> +#if defined(CONFIG_SPIN_TABLE)
> + branch_if_master x0, x1, master_cpu
> + b spin_table_secondary_jump
> + /* never return */
> +#elif defined(CONFIG_ARMV8_MULTIENTRY)
> branch_if_master x0, x1, master_cpu
>
> /*
> @@ -106,10 +110,8 @@ slave_cpu:
> ldr x0, [x1]
> cbz x0, slave_cpu
> br x0 /* branch to the given address */
> -master_cpu:
> - /* On the master CPU */
> #endif /* CONFIG_ARMV8_MULTIENTRY */
> -
> +master_cpu:
> bl _main
>
> #ifdef CONFIG_SYS_RESET_SCTRL
> diff --git a/arch/arm/lib/bootm-fdt.c b/arch/arm/lib/bootm-fdt.c
> index 76b75d8..ec581ac 100644
> --- a/arch/arm/lib/bootm-fdt.c
> +++ b/arch/arm/lib/bootm-fdt.c
> @@ -21,6 +21,7 @@
> #include <asm/armv7.h>
> #endif
> #include <asm/psci.h>
> +#include <spin_table.h>
>
> DECLARE_GLOBAL_DATA_PTR;
>
> @@ -51,5 +52,11 @@ int arch_fixup_fdt(void *blob)
> return ret;
> #endif
>
> +#ifdef CONFIG_SPIN_TABLE
> + ret = spin_table_update_dt(blob);
> + if (ret)
> + return ret;
> +#endif
> +
> return 0;
> }
> diff --git a/common/Makefile b/common/Makefile
> index 1557a04..f4eb381 100644
> --- a/common/Makefile
> +++ b/common/Makefile
> @@ -141,6 +141,7 @@ obj-$(CONFIG_ANDROID_BOOT_IMAGE) += image-android.o
> obj-$(CONFIG_$(SPL_)OF_LIBFDT) += image-fdt.o
> obj-$(CONFIG_$(SPL_)FIT) += image-fit.o
> obj-$(CONFIG_$(SPL_)FIT_SIGNATURE) += image-sig.o
> +obj-$(CONFIG_$(SPL_)SPIN_TABLE) += spin_table.o
> obj-$(CONFIG_IO_TRACE) += iotrace.o
> obj-y += memsize.o
> obj-y += stdio.o
> diff --git a/common/spin_table.c b/common/spin_table.c
> new file mode 100644
> index 0000000..046af8f
> --- /dev/null
> +++ b/common/spin_table.c
> @@ -0,0 +1,62 @@
> +/*
> + * Copyright (C) 2016 Masahiro Yamada <yamada.masah...@socionext.com>
> + *
> + * SPDX-License-Identifier: GPL-2.0+
> + */
> +
> +#include <common.h>
> +#include <libfdt.h>
> +#include <spin_table.h>
> +
> +int spin_table_update_dt(void *fdt)
> +{
> + int cpus_offset, offset;
> + const char *prop;
> + int ret;
> + unsigned long rsv_addr = (unsigned long)&spin_table_reserve_begin;
> + unsigned long rsv_size = &spin_table_reserve_end -
> + &spin_table_reserve_begin;
> +
> + cpus_offset = fdt_path_offset(fdt, "/cpus");
> + if (cpus_offset < 0)
> + return -ENODEV;
> +
> + for (offset = fdt_first_subnode(fdt, cpus_offset);
> + offset >= 0;
> + offset = fdt_next_subnode(fdt, offset)) {
> + prop = fdt_getprop(fdt, offset, "device_type", NULL);
> + if (!prop || strcmp(prop, "cpu"))
> + continue;
> +
> + /*
> + * In the first loop, we check if every CPU node specifies
> + * spin-table. Otherwise, just return successfully to not
> + * disturb other methods, like psci.
> + */
> + prop = fdt_getprop(fdt, offset, "enable-method", NULL);
> + if (!prop || strcmp(prop, "spin-table"))
> + return 0;
> + }
> +
> + for (offset = fdt_first_subnode(fdt, cpus_offset);
> + offset >= 0;
> + offset = fdt_next_subnode(fdt, offset)) {
> + prop = fdt_getprop(fdt, offset, "device_type", NULL);
> + if (!prop || strcmp(prop, "cpu"))
> + continue;
> +
> + ret = fdt_setprop_u64(fdt, offset, "cpu-release-addr",
> + (unsigned long)&spin_table_cpu_release_addr);
> + if (ret)
> + return -ENOSPC;
> + }
> +
> + ret = fdt_add_mem_rsv(fdt, rsv_addr, rsv_size);
> + if (ret)
> + return -ENOSPC;
> +
> + printf(" Reserved memory region for spin-table: addr=%lx size=%lx\n",
> + rsv_addr, rsv_size);
> +
> + return 0;
> +}
> diff --git a/include/spin_table.h b/include/spin_table.h
> new file mode 100644
> index 0000000..cf455a1
> --- /dev/null
> +++ b/include/spin_table.h
> @@ -0,0 +1,14 @@
> +/*
> + * SPDX-License-Identifier: GPL-2.0+
> + */
> +
> +#ifndef __SPIN_TABLE_H__
> +#define __SPIN_TABLE_H__
> +
> +extern u64 spin_table_cpu_release_addr;
> +extern char spin_table_reserve_begin;
> +extern char spin_table_reserve_end;
> +
> +int spin_table_update_dt(void *fdt);
> +
> +#endif /* __SPIN_TABLE_H__ */
> --
> 1.9.1
>
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