Unverified Commit 6216182f authored by Conor Dooley's avatar Conor Dooley Committed by Alexandre Ghiti
Browse files

RISC-V: clarify what some RISCV_ISA* config options do 

During some discussion on IRC yesterday and on Pu's bpf patch [1]
I noticed that these RISCV_ISA* Kconfig options are not really clear
about their implications. Many of these options have no impact on what
userspace is allowed to do, for example an application can use Zbb
regardless of whether or not the kernel does. Change the help text to
try and clarify whether or not an option affects just the kernel, or
also userspace. None of these options actually control whether or not an
extension is detected dynamically as that's done regardless of Kconfig
options, so drop any text that implies the option is required for
dynamic detection, rewording them as "do x when y is detected".

Link: https://lore.kernel.org/linux-riscv/20240328-ferocity-repose-c554f75a676c@spud/

 [1]
Reviewed-by: default avatarAndrew Jones <ajones@ventanamicro.com>
Signed-off-by: default avatarConor Dooley <conor.dooley@microchip.com>
Reviewed-by: default avatarCharlie Jenkins <charlie@rivosinc.com>
Reviewed-by: default avatarSamuel Holland <samuel.holland@sifive.com>
Link: https://lore.kernel.org/r/20241024-overdue-slogan-0b0f69d3da91@spud


Signed-off-by: default avatarAlexandre Ghiti <alexghiti@rivosinc.com>
parent 4295f4cc

arch/riscv/Kconfig

+19 −17
Original line number Diff line number Diff line
@@ -527,7 +527,8 @@ config RISCV_ISA_C 
	help

	  Adds "C" to the ISA subsets that the toolchain is allowed to emit

	  when building Linux, which results in compressed instructions in the

	  Linux binary.

	  Linux binary. This option produces a kernel that will not run on

	  systems that do not support compressed instructions.



	  If you don't know what to do here, say Y.
@@ -537,8 +538,8 @@ config RISCV_ISA_SVNAPOT 
	depends on RISCV_ALTERNATIVE

	default y

	help

	  Allow kernel to detect the Svnapot ISA-extension dynamically at boot

	  time and enable its usage.

	  Enable support for the Svnapot ISA-extension when it is detected

	  at boot.



	  The Svnapot extension is used to mark contiguous PTEs as a range

	  of contiguous virtual-to-physical translations for a naturally
@@ -556,9 +557,8 @@ config RISCV_ISA_SVPBMT 
	depends on RISCV_ALTERNATIVE

	default y

	help

	   Adds support to dynamically detect the presence of the Svpbmt

	   ISA-extension (Supervisor-mode: page-based memory types) and

	   enable its usage.

	   Add support for the Svpbmt ISA-extension (Supervisor-mode:

	   page-based memory types) in the kernel when it is detected at boot.



	   The memory type for a page contains a combination of attributes

	   that indicate the cacheability, idempotency, and ordering
@@ -577,14 +577,15 @@ config TOOLCHAIN_HAS_V 
	depends on AS_HAS_OPTION_ARCH



config RISCV_ISA_V

	bool "VECTOR extension support"

	bool "Vector extension support"

	depends on TOOLCHAIN_HAS_V

	depends on FPU

	select DYNAMIC_SIGFRAME

	default y

	help

	  Say N here if you want to disable all vector related procedure

	  in the kernel.

	  Add support for the Vector extension when it is detected at boot.

	  When this option is disabled, neither the kernel nor userspace may

	  use vector procedures.



	  If you don't know what to do here, say Y.
@@ -667,8 +668,8 @@ config RISCV_ISA_ZBB 
	depends on RISCV_ALTERNATIVE

	default y

	help

	   Adds support to dynamically detect the presence of the ZBB

	   extension (basic bit manipulation) and enable its usage.

	   Add support for enabling optimisations in the kernel when the

	   Zbb extension is detected at boot.



	   The Zbb extension provides instructions to accelerate a number

	   of bit-specific operations (count bit population, sign extending,
@@ -707,9 +708,9 @@ config RISCV_ISA_ZICBOM 
	select RISCV_DMA_NONCOHERENT

	select DMA_DIRECT_REMAP

	help

	   Adds support to dynamically detect the presence of the ZICBOM

	   extension (Cache Block Management Operations) and enable its

	   usage.

	   Add support for the Zicbom extension (Cache Block Management

	   Operations) and enable its use in the kernel when it is detected

	   at boot.



	   The Zicbom extension can be used to handle for example

	   non-coherent DMA support on devices that need it.
@@ -722,7 +723,7 @@ config RISCV_ISA_ZICBOZ 
	default y

	help

	   Enable the use of the Zicboz extension (cbo.zero instruction)

	   when available.

	   in the kernel when it is detected at boot.



	   The Zicboz extension is used for faster zeroing of memory.
@@ -760,8 +761,9 @@ config FPU 
	bool "FPU support"

	default y

	help

	  Say N here if you want to disable all floating-point related procedure

	  in the kernel.

	  Add support for floating point operations when an FPU is detected at

	  boot. When this option is disabled, neither the kernel nor userspace

	  may use the floating point unit.



	  If you don't know what to do here, say Y.