[PATCH v3] RISC-V: Add CONFIG_{NON,}PORTABLE

[Palmer Dabbelt <palmer@rivosinc.com>]

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
-- 
2.34.1