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Date: Fri, 12 Apr 2024 12:39:15 +0100
From: Conor Dooley <conor.dooley@microchip.com>
To: Charlie Jenkins <charlie@rivosinc.com>
CC: Conor Dooley <conor@kernel.org>, Rob Herring <robh@kernel.org>, Krzysztof
 Kozlowski <krzysztof.kozlowski+dt@linaro.org>, Paul Walmsley
	<paul.walmsley@sifive.com>, Palmer Dabbelt <palmer@dabbelt.com>, Albert Ou
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	<cleger@rivosinc.com>, Jonathan Corbet <corbet@lwn.net>, Shuah Khan
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Subject: Re: [PATCH 16/19] riscv: hwprobe: Add vendor extension probing
Message-ID: <20240412-candle-duffel-a612bab6e2a7@wendy>
References: <20240411-dev-charlie-support_thead_vector_6_9-v1-0-4af9815ec746@rivosinc.com>
 <20240411-dev-charlie-support_thead_vector_6_9-v1-16-4af9815ec746@rivosinc.com>
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On Thu, Apr 11, 2024 at 09:11:22PM -0700, Charlie Jenkins wrote:

> +static void hwprobe_isa_vendor_ext0(struct riscv_hwprobe *pair,
> +				    const struct cpumask *cpus)
> +{
> +	int cpu;
> +	u64 missing = 0;
> +
> +	pair->value = 0;
> +
> +	struct riscv_hwprobe mvendorid = {
> +		.key = RISCV_HWPROBE_KEY_MVENDORID,
> +		.value = 0
> +	};
> +
> +	hwprobe_arch_id(&mvendorid, cpus);
> +
> +	/* Set value to zero if CPUs in the set do not have the same vendor. */
> +	if (mvendorid.value == -1ULL)
> +		return;
> +
> +	/*
> +	 * Loop through and record vendor extensions that 1) anyone has, and
> +	 * 2) anyone doesn't have.
> +	 */
> +	for_each_cpu(cpu, cpus) {
> +		struct riscv_isainfo *isavendorinfo = &hart_isa_vendor[cpu];
> +
> +#define VENDOR_EXT_KEY(ext)								\
> +	do {										\
> +		if (__riscv_isa_vendor_extension_available(isavendorinfo->isa,		\
> +							 RISCV_ISA_VENDOR_EXT_##ext))	\
> +			pair->value |= RISCV_HWPROBE_VENDOR_EXT_##ext;			\
> +		else									\
> +			missing |= RISCV_HWPROBE_VENDOR_EXT_##ext;			\
> +	} while (false)
> +
> +	/*
> +	 * Only use VENDOR_EXT_KEY() for extensions which can be exposed to userspace,
> +	 * regardless of the kernel's configuration, as no other checks, besides
> +	 * presence in the hart_vendor_isa bitmap, are made.
> +	 */
> +	VENDOR_EXT_KEY(XTHEADVECTOR);

Reading the comment here, I don't think you can do this. All vector
support in userspace is continent on kernel configuration options.

> +
> +#undef VENDOR_EXT_KEY
> +	}
> +
> +	/* Now turn off reporting features if any CPU is missing it. */
> +	pair->value &= ~missing;
> +}

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