linux-kernel - [PATCH] ACPI: battery: use cache

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Date:   Sat, 14 Jul 2018 15:38:29 -0700
From:   Lucas Magasweran <lucas.magasweran@...e.org>
To:     linux-acpi@...r.kernel.org
Cc:     Vladimir Lebedev <vladimir.p.lebedev@...el.com>,
        Lucas Rangit Magasweran <lucas.magasweran@...e.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH] ACPI: battery: use cache_time as cache "enabled"

From: Lucas Rangit Magasweran <lucas.magasweran@...e.org>

When battery state is not cached the module parameter cache_time is 0
and battery->update_time starts at 0. However, it set to jiffies in
each call to acpi_battery_get_state() and should not be used to
determine if a cache time is used.

Using battery->update_time causes the evaluation of time_before()
even though cache_time is 0.

This is a minor issue as the behavior is still as expected.
Even if kernel HZ was very slow and jiffies remained equal, the
expected branch (false) would be taken because time_before() is
used instead of time_before_eq().

Signed-off-by: Lucas Rangit Magasweran <lucas.magasweran@...e.org>
---
 drivers/acpi/battery.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
index d79ad84..f88bc9f 100644
--- a/drivers/acpi/battery.c
+++ b/drivers/acpi/battery.c
@@ -549,7 +549,7 @@ static int acpi_battery_get_state(struct acpi_battery *battery)
 	if (!acpi_battery_present(battery))
 		return 0;

-	if (battery->update_time &&
+	if (cache_time &&
 	    time_before(jiffies, battery->update_time +
 			msecs_to_jiffies(cache_time)))
 		return 0;
-- 
2.7.4