hwmon: (pwm-fan) Implement after shutdown fan settings

Add fan-shutdown-percent property, used to describe fan RPM in percent set
during shutdown. This is used to keep the fan running at fixed RPM after
the kernel shut down, which is useful on hardware that does keep heating
itself even after the kernel did shut down, for example from some sort of
management core. The current behavior of pwm-fan is to unconditionally
stop the fan on shutdown, which is not always the safe and correct thing
to do, so let the hardware description include the expected behavior.

Signed-off-by: Marek Vasut <[e-mail]>
Tested-by: Wolfram Sang <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>

drivers/hwmon/pwm-fan.c

···
 
 	u64 pwm_duty_cycle_from_stopped;
 	u32 pwm_usec_from_stopped;
+	u8 pwm_shutdown;
 };
 
 /* This handler assumes self resetting edge triggered interrupt. */
···
 	struct pwm_fan_ctx *ctx = __ctx;
 
 	timer_delete_sync(&ctx->rpm_timer);
-	/* Switch off everything */
-	ctx->enable_mode = pwm_disable_reg_disable;
-	pwm_fan_power_off(ctx, true);
+	if (ctx->pwm_shutdown) {
+		ctx->enable_mode = pwm_enable_reg_enable;
+		__set_pwm(ctx, ctx->pwm_shutdown);
+	} else {
+		/* Switch off everything */
+		ctx->enable_mode = pwm_disable_reg_disable;
+		pwm_fan_power_off(ctx, true);
+	}
 }
 
 static int pwm_fan_probe(struct platform_device *pdev)
···
 	int ret;
 	const struct hwmon_channel_info **channels;
 	u32 initial_pwm, pwm_min_from_stopped = 0;
+	u32 pwm_shutdown_percent = 0;
 	u32 *fan_channel_config;
 	int channel_count = 1;	/* We always have a PWM channel. */
 	int i;
···
 
 		channels[1] = &ctx->fan_channel;
 	}
+
+	ret = device_property_read_u32(dev, "fan-shutdown-percent",
+				       &pwm_shutdown_percent);
+	if (!ret && pwm_shutdown_percent)
+		ctx->pwm_shutdown = (clamp(pwm_shutdown_percent, 0, 100) * 255) / 100;
 
 	ret = device_property_read_u32(dev, "fan-stop-to-start-percent",
 				       &pwm_min_from_stopped);