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[v9,23/40] arm64/sme: Disable streaming mode and ZA when flushing CPU state

Message ID 20220126151120.3811248-24-broonie@kernel.org (mailing list archive)
State Accepted
Commit d45d7ff7047f7f6c3221b0f028fade640812f931
Headers show
Series arm64/sme: Initial support for the Scalable Matrix Extension | expand

Commit Message

Mark Brown Jan. 26, 2022, 3:11 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 <broonie@kernel.org>
---
 arch/arm64/kernel/fpsimd.c | 9 +++++++++
 1 file changed, 9 insertions(+)
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Patch

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 8b111b7f2006..e00d3a9e919c 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1762,6 +1762,15 @@  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 increase power
+	 * consumption.
+	 */
+	if (system_supports_sme())
+		sme_smstop();
+
 	set_thread_flag(TIF_FOREIGN_FPSTATE);
 }