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Date:   Thu, 14 Jul 2022 14:26:10 -0700 (PDT)
Subject:     Re: [PATCH v3] RISC-V: Add CONFIG_{NON,}PORTABLE
In-Reply-To: <20220521193356.26562-1-palmer@rivosinc.com>
CC:     Paul Walmsley <paul.walmsley@sifive.com>, aou@eecs.berkeley.edu,
        rdunlap@infradead.org, Arnd Bergmann <arnd@arndb.de>,
        anup@brainfault.org, alexandre.ghiti@canonical.com,
        damien.lemoal@opensource.wdc.com,
        Atish Patra <atishp@rivosinc.com>, axboe@kernel.dk,
        guoren@kernel.org, mchitale@ventanamicro.com,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux@rivosinc.com
From:   Palmer Dabbelt <palmer@rivosinc.com>
To:     linux-riscv@lists.infradead.org
Message-ID: <mhng-b5cae221-396d-49a6-91b2-362f490ca732@palmer-ri-x1c9>
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On Sat, 21 May 2022 12:33:57 PDT (-0700), Palmer Dabbelt wrote:
> From: Palmer Dabbelt <palmer@rivosinc.com>
>
> The RISC-V port has collected a handful of options that are
> fundamentally non-portable.  To prevent users from shooting themselves
> in the foot, hide them all behind a config entry that explicitly calls
> out that non-portable binaries may be produced.
>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> Reviewed-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> ---
> Changes since v2:
>
> * Update the nommu and rv32 defconfigs.  I'm still getting some ugliness
>   like
>
>     $ make.riscv rv32_defconfig
>     *** Default configuration is based on 'defconfig'
>     #
>     # configuration written to .config
>     #
>     Using .config as base
>     Merging ./arch/riscv/configs/32-bit.config
>     Value of CONFIG_PORTABLE is redefined by fragment ./arch/riscv/configs/32-bit.config:
>     Previous value: CONFIG_PORTABLE=y
>     New value: # CONFIG_PORTABLE is not set
>
>     Value of CONFIG_NONPORTABLE is redefined by fragment ./arch/riscv/configs/32-bit.config:
>     Previous value: # CONFIG_NONPORTABLE is not set
>     New value: CONFIG_NONPORTABLE=y
>
>     #
>     # merged configuration written to .config (needs make)
>     #
>     .config:3831:warning: override: ARCH_RV32I changes choice state
>     #
>     # configuration written to .config
>     #
>
>   not sure if there's a better way to do this.
>
> Changes since v1:
>
> * Fix a bunch of spelling mistakes.
> * Move NONPORTABLE under the "Platform type" sub-heading.
> * Fix the rv32i dependency.
>
> ---
>  arch/riscv/Kconfig                            | 28 +++++++++++++++++--
>  arch/riscv/configs/32-bit.config              |  2 ++
>  arch/riscv/configs/nommu_k210_defconfig       |  1 +
>  .../riscv/configs/nommu_k210_sdcard_defconfig |  1 +
>  arch/riscv/configs/nommu_virt_defconfig       |  1 +
>  arch/riscv/configs/rv32_defconfig             |  1 +
>  6 files changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index f863065b478c..cd67b09a80f5 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -222,6 +222,21 @@ source "arch/riscv/Kconfig.erratas"
>
>  menu "Platform type"
>
> +config NONPORTABLE
> +	bool "Allow configurations that result in non-portable kernels"
> +	help
> +	  RISC-V kernel binaries are compatible between all known systems
> +	  whenever possible, but there are some use cases that can only be
> +	  satisfied by configurations that result in kernel binaries that are
> +	  not portable between systems.
> +
> +	  Selecting N does not guarantee kernels will be portable to all known
> +	  systems.  Selecting any of the options guarded by NONPORTABLE will
> +	  result in kernel binaries that are unlikely to be portable between
> +	  systems.
> +
> +	  If unsure, say N.
> +
>  choice
>  	prompt "Base ISA"
>  	default ARCH_RV64I
> @@ -231,6 +246,7 @@ choice
>
>  config ARCH_RV32I
>  	bool "RV32I"
> +	depends on NONPORTABLE
>  	select 32BIT
>  	select GENERIC_LIB_ASHLDI3
>  	select GENERIC_LIB_ASHRDI3
> @@ -541,6 +557,7 @@ config STACKPROTECTOR_PER_TASK
>
>  config PHYS_RAM_BASE_FIXED
>  	bool "Explicitly specified physical RAM address"
> +	depends on NONPORTABLE
>  	default n
>
>  config PHYS_RAM_BASE
> @@ -554,7 +571,7 @@ config PHYS_RAM_BASE
>
>  config XIP_KERNEL
>  	bool "Kernel Execute-In-Place from ROM"
> -	depends on MMU && SPARSEMEM
> +	depends on MMU && SPARSEMEM && NONPORTABLE
>  	# This prevents XIP from being enabled by all{yes,mod}config, which
>  	# fail to build since XIP doesn't support large kernels.
>  	depends on !COMPILE_TEST
> @@ -594,9 +611,16 @@ endmenu
>
>  config BUILTIN_DTB
>  	bool
> -	depends on OF
> +	depends on OF && NONPORTABLE
>  	default y if XIP_KERNEL
>
> +config PORTABLE
> +	bool
> +	default !NONPORTABLE
> +	select EFI
> +	select OF
> +	select MMU
> +
>  menu "Power management options"
>
>  source "kernel/power/Kconfig"
> diff --git a/arch/riscv/configs/32-bit.config b/arch/riscv/configs/32-bit.config
> index 43f41323b67e..f6af0f708df4 100644
> --- a/arch/riscv/configs/32-bit.config
> +++ b/arch/riscv/configs/32-bit.config
> @@ -1,2 +1,4 @@
>  CONFIG_ARCH_RV32I=y
>  CONFIG_32BIT=y
> +# CONFIG_PORTABLE is not set
> +CONFIG_NONPORTABLE=y
> diff --git a/arch/riscv/configs/nommu_k210_defconfig b/arch/riscv/configs/nommu_k210_defconfig
> index 2438fa39f8ae..96fe8def644c 100644
> --- a/arch/riscv/configs/nommu_k210_defconfig
> +++ b/arch/riscv/configs/nommu_k210_defconfig
> @@ -28,6 +28,7 @@ CONFIG_EMBEDDED=y
>  CONFIG_SLOB=y
>  # CONFIG_MMU is not set
>  CONFIG_SOC_CANAAN=y
> +CONFIG_NONPORTABLE=y
>  CONFIG_SMP=y
>  CONFIG_NR_CPUS=2
>  CONFIG_CMDLINE="earlycon console=ttySIF0"
> diff --git a/arch/riscv/configs/nommu_k210_sdcard_defconfig b/arch/riscv/configs/nommu_k210_sdcard_defconfig
> index 9a133e63ae5b..379740654373 100644
> --- a/arch/riscv/configs/nommu_k210_sdcard_defconfig
> +++ b/arch/riscv/configs/nommu_k210_sdcard_defconfig
> @@ -20,6 +20,7 @@ CONFIG_EMBEDDED=y
>  CONFIG_SLOB=y
>  # CONFIG_MMU is not set
>  CONFIG_SOC_CANAAN=y
> +CONFIG_NONPORTABLE=y
>  CONFIG_SMP=y
>  CONFIG_NR_CPUS=2
>  CONFIG_CMDLINE="earlycon console=ttySIF0 root=/dev/mmcblk0p1 rootwait ro"
> diff --git a/arch/riscv/configs/nommu_virt_defconfig b/arch/riscv/configs/nommu_virt_defconfig
> index 5269fbb6b4fc..1a56eda5ce46 100644
> --- a/arch/riscv/configs/nommu_virt_defconfig
> +++ b/arch/riscv/configs/nommu_virt_defconfig
> @@ -25,6 +25,7 @@ CONFIG_EXPERT=y
>  CONFIG_SLOB=y
>  # CONFIG_MMU is not set
>  CONFIG_SOC_VIRT=y
> +CONFIG_NONPORTABLE=y
>  CONFIG_SMP=y
>  CONFIG_CMDLINE="root=/dev/vda rw earlycon=uart8250,mmio,0x10000000,115200n8 console=ttyS0"
>  CONFIG_CMDLINE_FORCE=y
> diff --git a/arch/riscv/configs/rv32_defconfig b/arch/riscv/configs/rv32_defconfig
> index 7e5efdc3829d..77bdb1d05a88 100644
> --- a/arch/riscv/configs/rv32_defconfig
> +++ b/arch/riscv/configs/rv32_defconfig
> @@ -18,6 +18,7 @@ CONFIG_EXPERT=y
>  CONFIG_PROFILING=y
>  CONFIG_SOC_SIFIVE=y
>  CONFIG_SOC_VIRT=y
> +CONFIG_NONPORTABLE=y
>  CONFIG_ARCH_RV32I=y
>  CONFIG_SMP=y
>  CONFIG_HOTPLUG_CPU=y

This is on for-next.