[PATCH 4.15 152/202] media: dt-bindings/media/cec-gpio.txt: mention the CEC/HPD max voltages

[Greg Kroah-Hartman]

4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hans Verkuil <hverkuil@xxxxxxxxx>

commit dac15ed62dc9d7898d3695a3c393d6f712d66185 upstream.

Mention the maximum voltages of the CEC and HPD lines. Since in the example
these lines are connected to a Raspberry Pi and the Rpi GPIO lines are 3.3V
it is a good idea to warn against directly connecting the HPD to the Raspberry
Pi's GPIO line.

Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
Reviewed-by: Rob Herring <robh@xxxxxxxxxx>
Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 Documentation/devicetree/bindings/media/cec-gpio.txt |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/Documentation/devicetree/bindings/media/cec-gpio.txt
+++ b/Documentation/devicetree/bindings/media/cec-gpio.txt
@@ -4,6 +4,10 @@ The HDMI CEC GPIO module supports CEC im
 is hooked up to a pull-up GPIO line and - optionally - the HPD line is
 hooked up to another GPIO line.
 
+Please note: the maximum voltage for the CEC line is 3.63V, for the HPD
+line it is 5.3V. So you may need some sort of level conversion circuitry
+when connecting them to a GPIO line.
+
 Required properties:
   - compatible: value must be "cec-gpio".
   - cec-gpios: gpio that the CEC line is connected to. The line should be
@@ -21,7 +25,7 @@ the following property is optional:
 
 Example for the Raspberry Pi 3 where the CEC line is connected to
 pin 26 aka BCM7 aka CE1 on the GPIO pin header and the HPD line is
-connected to pin 11 aka BCM17:
+connected to pin 11 aka BCM17 (some level shifter is needed for this!):
 
 #include <dt-bindings/gpio/gpio.h>