linux-kernel - [PATCH] hwmon: (gpio-fan) Remove un-necessary speed

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Date:	Fri, 19 Feb 2016 18:09:51 -0600
From:	Nishanth Menon <nm@...com>
To:	Guenter Roeck <linux@...ck-us.net>,
	Jean Delvare <jdelvare@...e.com>
CC:	Tony Lindgren <tony@...mide.com>, <linux-kernel@...r.kernel.org>,
	<lm-sensors@...sensors.org>, <linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, Nishanth Menon <nm@...com>,
	Eduardo Valentin <edubezval@...il.com>
Subject: [PATCH] hwmon: (gpio-fan) Remove un-necessary speed_index lookup for thermal hook

Thermal hook gpio_fan_get_cur_state is only interested in knowing
the current speed index that was setup in the system, this is
already available as part of fan_data->speed_index which is always
set by set_fan_speed. Using get_fan_speed_index is useful when we
have no idea about the fan speed configuration (for example during
fan_ctrl_init).

When thermal framework invokes
gpio_fan_get_cur_state=>get_fan_speed_index via gpio_fan_get_cur_state
especially in a polled configuration for thermal governor, we
basically hog the i2c interface to the extent that other functions
fail to get any traffic out :(.

Instead, just provide the last state set in the driver - since the gpio
fan driver is responsible for the fan state immaterial of override, the
fan_data->speed_index should accurately reflect the state.

Fixes: b5cf88e46bad ("(gpio-fan): Add thermal control hooks")

Reported-by: Tony Lindgren <tony@...mide.com>
Cc: Guenter Roeck <linux@...ck-us.net>
Cc: Eduardo Valentin <edubezval@...il.com>
Signed-off-by: Nishanth Menon <nm@...com>
---
Test logs from linus master  v4.5-rc4-137-g23300f657594 
Without fix: http://paste.ubuntu.org.cn/3948618
With Fix: http://paste.ubuntu.org.cn/3948617

 drivers/hwmon/gpio-fan.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/drivers/hwmon/gpio-fan.c b/drivers/hwmon/gpio-fan.c
index 82de3deeb18a..685568b1236d 100644
--- a/drivers/hwmon/gpio-fan.c
+++ b/drivers/hwmon/gpio-fan.c
@@ -406,16 +406,11 @@ static int gpio_fan_get_cur_state(struct thermal_cooling_device *cdev,
 				  unsigned long *state)
 {
 	struct gpio_fan_data *fan_data = cdev->devdata;
-	int r;

 	if (!fan_data)
 		return -EINVAL;

-	r = get_fan_speed_index(fan_data);
-	if (r < 0)
-		return r;
-
-	*state = r;
+	*state = fan_data->speed_index;
 	return 0;
 }

-- 
2.7.0