[PATCH 0/2] efi: Allow to auto-disable it on RT

[PATCH 0/2] efi: Allow to auto-disable it on RT

[Sebastian Andrzej Siewior]

Hi,

since we have CONFIG_PREEMPT_RT these two patches allow to auto-disable
EFI runtime services on RT while it is still possible to override it and
use it if needed.

Sebastian

[PATCH 1/2] efi: Allow efi=runtime

[Sebastian Andrzej Siewior]

In case the option "efi=noruntime" is default at built-time, the user
could overwrite its state by `efi=runtime' and allow it again.

Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/firmware/efi/efi.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -114,6 +114,9 @@ static int __init parse_efi_cmdline(char
 	if (parse_option_str(str, "noruntime"))
 		disable_runtime = true;
 
+	if (parse_option_str(str, "runtime"))
+		disable_runtime = false;
+
 	return 0;
 }
 early_param("efi", parse_efi_cmdline);

[PATCH 2/2] efi: Disable runtime services on RT

[Sebastian Andrzej Siewior]

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(-)

--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -88,7 +88,7 @@ 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;