[PATCH v3 2/2] arm64: Support systems without FP/ASIMD

On 14/11/16 11:48, Catalin Marinas wrote:

Hi Suzuki,

quoted

+static inline bool system_supports_fpsimd(void)
+{
+	return !cpus_have_const_cap(ARM64_HAS_NO_FPSIMD);
+}

Any particular reason why using negation instead of a ARM64_HAS_FPSIMD?
A potential problem would be the default cpus_have_const_cap()
implementation and the default static key having a slight performance
impact.

The negation was chosen to avoid hotpatching in the most common case.
But as you said, it has an impact on the other side. I think doing
a one time hotpatching at boot time is more optimal than penalising
a bunch of other users throughout the execution. I will take a look
at changing it back to a ARM64_HAS_FPSIMD.

quoted

 	},
+	{
+		/* FP/SIMD is not implemented */
+		.capability = ARM64_HAS_NO_FPSIMD,
+		.def_scope = SCOPE_SYSTEM,
+		.min_field_value = 0,
+		.matches = has_no_fpsimd,
+	},

If we go for negation, I don't think we need a min_field_value at all,
the matching is done by the has_no_fpsimd() function.

You're right.

Suzuki