Re: [PATCH v4 3/6] RISC-V: hwprobe: Add support for RISCV_HWPROBE_BASE_BEHAVIOR_IMA

From: Conor Dooley <conor@kernel.org>
To: Evan Green <evan@rivosinc.com>
Cc: Palmer Dabbelt <palmer@rivosinc.com>,
	slewis@rivosinc.com, heiko@sntech.de, vineetg@rivosinc.com,
	Conor Dooley <conor.dooley@microchip.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Andrew Bresticker <abrestic@rivosinc.com>,
	Celeste Liu <coelacanthus@outlook.com>,
	Guo Ren <guoren@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org
Subject: Re: [PATCH v4 3/6] RISC-V: hwprobe: Add support for RISCV_HWPROBE_BASE_BEHAVIOR_IMA
Date: Wed, 22 Mar 2023 15:35:59 +0000	[thread overview]
Message-ID: <8e132bed-c85a-4bfd-bff8-5147db1cec32@spud> (raw)
In-Reply-To: <20230314183220.513101-4-evan@rivosinc.com>

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On Tue, Mar 14, 2023 at 11:32:17AM -0700, Evan Green wrote:
> We have an implicit set of base behaviors that userspace depends on,
> which are mostly defined in various ISA specifications.
> 
> Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Evan Green <evan@rivosinc.com>
> Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

> @@ -125,6 +126,25 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>  	case RISCV_HWPROBE_KEY_MIMPID:
>  		hwprobe_arch_id(pair, cpus);
>  		break;
> +	/*
> +	 * The kernel already assumes that the base single-letter ISA
> +	 * extensions are supported on all harts, and only supports the
> +	 * IMA base, so just cheat a bit here and tell that to
> +	 * userspace.
> +	 */
> +	case RISCV_HWPROBE_KEY_BASE_BEHAVIOR:
> +		pair->value = RISCV_HWPROBE_BASE_BEHAVIOR_IMA;
> +		break;
> +
> +	case RISCV_HWPROBE_KEY_IMA_EXT_0:
> +		pair->value = 0;
> +		if (has_fpu())
> +			pair->value |= RISCV_HWPROBE_IMA_FD;
> +
> +		if (elf_hwcap & RISCV_ISA_EXT_c)

Random thought while reviewing another patch, and I kinda felt a bit
stupid following the existing code to try and make sure, but should this
become a call to riscv_isa_extension_available(NULL, c)?
It may be nice to propagate that helper, if it works, than check the bit
directly.

Cheers,
Conor.

> +			pair->value |= RISCV_HWPROBE_IMA_C;
> +
> +		break;
>  
>  	/*
>  	 * For forward compatibility, unknown keys don't fail the whole
> -- 
> 2.25.1
> 

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