linux-kernel - Re: [PATCH V12 3/5] riscv: Add RISC-V Svrsw60t59b extension support

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Message-ID: <20250915-landowner-parsnip-d6778ee7208f@spud>
Date: Mon, 15 Sep 2025 18:03:53 +0100
From: Conor Dooley <conor@...nel.org>
To: Chunyan Zhang <zhangchunyan@...as.ac.cn>
Cc: linux-riscv@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>,
	Deepak Gupta <debug@...osinc.com>,
	Ved Shanbhogue <ved@...osinc.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Xu <peterx@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Axel Rasmussen <axelrasmussen@...gle.com>,
	Yuanchu Xie <yuanchu@...gle.com>,
	Chunyan Zhang <zhang.lyra@...il.com>
Subject: Re: [PATCH V12 3/5] riscv: Add RISC-V Svrsw60t59b extension support

On Mon, Sep 15, 2025 at 06:13:41PM +0800, Chunyan Zhang wrote:
> The Svrsw60t59b extension allows to free the PTE reserved bits 60
> and 59 for software to use.
> 
> Reviewed-by: Alexandre Ghiti <alexghiti@...osinc.com>
> Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
> Signed-off-by: Chunyan Zhang <zhangchunyan@...as.ac.cn>
> ---
>  arch/riscv/Kconfig             | 14 ++++++++++++++
>  arch/riscv/include/asm/hwcap.h |  1 +
>  arch/riscv/kernel/cpufeature.c |  1 +
>  3 files changed, 16 insertions(+)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 51dcd8eaa243..e1b6a95952c4 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -862,6 +862,20 @@ config RISCV_ISA_ZICBOP
>  
>  	  If you don't know what to do here, say Y.
>  
> +config RISCV_ISA_SVRSW60T59B
> +	bool "Svrsw60t59b extension support for using PTE bits 60 and 59"
> +	depends on MMU && 64BIT
> +	depends on RISCV_ALTERNATIVE
> +	default y
> +	help
> +	  Adds support to dynamically detect the presence of the Svrsw60t59b
> +	  extension and enable its usage.
> +
> +	  The Svrsw60t59b extension allows to free the PTE reserved bits 60
> +	  and 59 for software to use.
> +
> +	  If you don't know what to do here, say Y.
> +
>  config TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
>  	def_bool y
>  	# https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=aed44286efa8ae8717a77d94b51ac3614e2ca6dc
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index affd63e11b0a..f98fcb5c17d5 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -106,6 +106,7 @@
>  #define RISCV_ISA_EXT_ZAAMO		97
>  #define RISCV_ISA_EXT_ZALRSC		98
>  #define RISCV_ISA_EXT_ZICBOP		99
> +#define RISCV_ISA_EXT_SVRSW60T59B	100
>  
>  #define RISCV_ISA_EXT_XLINUXENVCFG	127
>  
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 743d53415572..2ba71d2d3fa3 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -539,6 +539,7 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
>  	__RISCV_ISA_EXT_DATA(svinval, RISCV_ISA_EXT_SVINVAL),
>  	__RISCV_ISA_EXT_DATA(svnapot, RISCV_ISA_EXT_SVNAPOT),
>  	__RISCV_ISA_EXT_DATA(svpbmt, RISCV_ISA_EXT_SVPBMT),
> +	__RISCV_ISA_EXT_DATA(svrsw60t59b, RISCV_ISA_EXT_SVRSW60T59B),
>  	__RISCV_ISA_EXT_DATA(svvptc, RISCV_ISA_EXT_SVVPTC),

If this is not ACPI only, than you need to document this in the
extensions dt-binding.

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