kselftest/arm64: add HWCAP test for FEAT_S1POE

Check that when POE is enabled, the POR_EL0 register is accessible.
Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240822151113.1479789-28-joey.gouly@arm.comSigned-off-by: Will Deacon <will@kernel.org>

tools/testing/selftests/arm64/abi/hwcap.c

@@ -156,6 +156,12 @@ static void pmull_sigill(void)
 	asm volatile(".inst 0x0ee0e000" : : : );
 }
 
+static void poe_sigill(void)
+{
+	/* mrs x0, POR_EL0 */
+	asm volatile("mrs x0, S3_3_C10_C2_4" : : : "x0");
+}
+
 static void rng_sigill(void)
 {
 	asm volatile("mrs x0, S3_3_C2_C4_0" : : : "x0");
@@ -601,6 +607,14 @@ static const struct hwcap_data {
 		.cpuinfo = "pmull",
 		.sigill_fn = pmull_sigill,
 	},
+	{
+		.name = "POE",
+		.at_hwcap = AT_HWCAP2,
+		.hwcap_bit = HWCAP2_POE,
+		.cpuinfo = "poe",
+		.sigill_fn = poe_sigill,
+		.sigill_reliable = true,
+	},
 	{
 		.name = "RNG",
 		.at_hwcap = AT_HWCAP2,