[v1,29/38] arm64/sme: Disable streaming mode and ZA when flushing CPU state

Commit Message

Mark Brown Sept. 30, 2021, 6:11 p.m. UTC

Both streaming mode and ZA may increase power consumption when they are
enabled and streaming mode makes many FPSIMD and SVE instructions undefined
which will cause problems for any kernel mode floating point so disable
both when we flush the CPU state. This covers both kernel_neon_begin() and
idle and after flushing the state a reload is always required anyway.

Signed-off-by: Mark Brown <[e-mail]>
---
 arch/arm64/kernel/fpsimd.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

Patch

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 118435dc1da4..c34d32360502 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1736,6 +1736,17 @@  static void fpsimd_flush_cpu_state(void)
 {
 	WARN_ON(!system_supports_fpsimd());
 	__this_cpu_write(fpsimd_last_state.st, NULL);
+
+	/*
+	 * Leaving streaming mode enabled will cause issues for any kernel
+	 * NEON and leaving streaming mode or ZA enabled may incrase power
+	 * consumption.
+	 */
+	if (system_supports_sme())
+		sysreg_clear_set_s(SYS_SVCR_EL0,
+				   SYS_SVCR_EL0_ZA_MASK | SYS_SVCR_EL0_ZA_MASK,
+				   0);
+
 	set_thread_flag(TIF_FOREIGN_FPSTATE);
 }