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From 8ff328d63beab0f17efde608bcaa09ff553a8e94 Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 26 Jul 2018 15:03:16 +0200
Subject: [PATCH 097/191] efi: Disable runtime services on RT
Based on meassurements the EFI functions get_variable /
get_next_variable take up to 2us which looks okay.
The functions get_time, set_time take around 10ms. Those 10ms are too
much. Even one ms would be too much.
Ard mentioned that SetVariable might even trigger larger latencies if
the firware will erase flash blocks on NOR.
The time-functions are used by efi-rtc and can be triggered during
runtimed (either via explicit read/write or ntp sync).
The variable write could be used by pstore.
These functions can be disabled without much of a loss. The poweroff /
reboot hooks may be provided by PSCI.
Disable EFI's runtime wrappers.
This was observed on "EFI v2.60 by SoftIron Overdrive 1000".
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
drivers/firmware/efi/efi.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index df3f9bcab581..1819da1c9fec 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -66,7 +66,7 @@ struct mm_struct efi_mm = {
struct workqueue_struct *efi_rts_wq;
-static bool disable_runtime;
+static bool disable_runtime = IS_ENABLED(CONFIG_PREEMPT_RT);
static int __init setup_noefi(char *arg)
{
disable_runtime = true;
--
2.19.1
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