linux-kernel - [PATCH 2/4] ACPI: PM: Remove redundant cache flushing

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Date:   Mon,  6 Dec 2021 15:29:50 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     rafael@...nel.org
Cc:     ak@...ux.intel.com, bp@...en8.de, dan.j.williams@...el.com,
        dave.hansen@...ux.intel.com, hpa@...or.com,
        kirill.shutemov@...ux.intel.com, knsathya@...nel.org,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, rjw@...ysocki.net,
        sathyanarayanan.kuppuswamy@...ux.intel.com, tglx@...utronix.de,
        tony.luck@...el.com, x86@...nel.org
Subject: [PATCH 2/4] ACPI: PM: Remove redundant cache flushing

ACPICA code takes care about cache flushing on S1/S2/S3 in
acpi_hw_extended_sleep() and acpi_hw_legacy_sleep().

acpi_suspend_enter() calls into ACPICA code via acpi_enter_sleep_state()
for S1 or x86_acpi_suspend_lowlevel() for S3. It only need to flush
cache for S2 (not sure if this call path is ever used for S2).

acpi_sleep_prepare() call tree:
  __acpi_pm_prepare()
    acpi_pm_prepare()
      acpi_suspend_ops::prepare_late()
      acpi_hibernation_ops::pre_snapshot()
      acpi_hibernation_ops::prepare()
    acpi_suspend_begin_old()
      acpi_suspend_begin_old::begin()
  acpi_hibernation_begin_old()
    acpi_hibernation_ops_old::acpi_hibernation_begin_old()
  acpi_power_off_prepare()
    pm_power_off_prepare()

Hibernation (S4) and Power Off (S5) don't require cache flushing. So,
the only interesting callsites are acpi_suspend_ops::prepare_late() and
acpi_suspend_begin_old::begin(). Both of them have cache flush on
->enter() operation in acpi_suspend_enter().

Remove redundant ACPI_FLUSH_CPU_CACHE() in acpi_sleep_prepare() and
acpi_suspend_enter().

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 drivers/acpi/sleep.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/sleep.c b/drivers/acpi/sleep.c
index eaa47753b758..14e8df0ac762 100644
--- a/drivers/acpi/sleep.c
+++ b/drivers/acpi/sleep.c
@@ -73,7 +73,6 @@ static int acpi_sleep_prepare(u32 acpi_state)
 		acpi_set_waking_vector(acpi_wakeup_address);
 
 	}
-	ACPI_FLUSH_CPU_CACHE();
 #endif
 	pr_info("Preparing to enter system sleep state S%d\n", acpi_state);
 	acpi_enable_wakeup_devices(acpi_state);
@@ -566,15 +565,15 @@ static int acpi_suspend_enter(suspend_state_t pm_state)
 	u32 acpi_state = acpi_target_sleep_state;
 	int error;
 
-	ACPI_FLUSH_CPU_CACHE();
-
 	trace_suspend_resume(TPS("acpi_suspend"), acpi_state, true);
 	switch (acpi_state) {
 	case ACPI_STATE_S1:
 		barrier();
 		status = acpi_enter_sleep_state(acpi_state);
 		break;
-
+	case ACPI_STATE_S2:
+		ACPI_FLUSH_CPU_CACHE();
+		break;
 	case ACPI_STATE_S3:
 		if (!acpi_suspend_lowlevel)
 			return -ENOSYS;
-- 
2.32.0