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[2/2] hwmon: (max6650) Add initial rpm target devicetree documentation

Message ID 1472026407-3448-2-git-send-email-mike.looijmans@topic.nl
State Not Applicable, archived
Headers show

Commit Message

Mike Looijmans Aug. 24, 2016, 8:13 a.m. UTC
Add devicetree property for early initialization of the fan controller
to prevent overheating, for example when resetting the board while the
fan was completely turned off.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
---
 Documentation/devicetree/bindings/hwmon/max6650.txt | 5 +++++
 1 file changed, 5 insertions(+)

Comments

Rob Herring Aug. 30, 2016, 4:38 p.m. UTC | #1
On Wed, Aug 24, 2016 at 10:13:27AM +0200, Mike Looijmans wrote:
> Add devicetree property for early initialization of the fan controller
> to prevent overheating, for example when resetting the board while the
> fan was completely turned off.
> 
> Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
> ---
>  Documentation/devicetree/bindings/hwmon/max6650.txt | 5 +++++
>  1 file changed, 5 insertions(+)

The kernel boot seems kind of late to ensure your fan is running, but

Acked-by: Rob Herring <robh@kernel.org>
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Mike Looijmans Aug. 30, 2016, 4:56 p.m. UTC | #2
On 30-08-16 18:38, Rob Herring wrote:
> On Wed, Aug 24, 2016 at 10:13:27AM +0200, Mike Looijmans wrote:
>> Add devicetree property for early initialization of the fan controller
>> to prevent overheating, for example when resetting the board while the
>> fan was completely turned off.
>>
>> Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
>> ---
>>   Documentation/devicetree/bindings/hwmon/max6650.txt | 5 +++++
>>   1 file changed, 5 insertions(+)
>
> The kernel boot seems kind of late to ensure your fan is running, but
>
> Acked-by: Rob Herring <robh@kernel.org>

Thanks!

Well, "late's better than never," my grandma used to say when we visited :)

To put your mind at ease, the particular platform I'm using this for is 
an xc7z045 (Zynq) where the ARMs running the Linux kernel will only 
account for 0.5W, but once the logic awakens the chip can dissipate up 
to 30W. The logic bitstream is usually on the rootfs, so kernel boot is 
early enough for the fan to start spinning. And with the logic asleep, 
it need not spin at all.
diff mbox

Patch

diff --git a/Documentation/devicetree/bindings/hwmon/max6650.txt b/Documentation/devicetree/bindings/hwmon/max6650.txt
index d6c10e3..f6bd87d 100644
--- a/Documentation/devicetree/bindings/hwmon/max6650.txt
+++ b/Documentation/devicetree/bindings/hwmon/max6650.txt
@@ -13,6 +13,10 @@  Optional properties, default is to retain the chip's current setting:
 - maxim,fan-prescale  : Pre-scaling value, as per datasheet [1]. Lower values
 			allow more fine-grained control of slower fans.
 			Valid: 1, 2, 4, 8, 16.
+- maxim,fan-target-rpm: Initial requested fan rotation speed. If specified, the
+			driver selects closed-loop mode and the requested speed.
+			This ensures the fan is already running before userspace
+			takes over.
 
 Example:
 	fan-max6650: max6650@1b {
@@ -20,4 +24,5 @@  Example:
 		compatible = "maxim,max6650";
 		maxim,fan-microvolt = <12000000>;
 		maxim,fan-prescale = <4>;
+		maxim,fan-target-rpm = <1200>;
 	};