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media: dt-bindings/media/cec-gpio.txt: mention the CEC/HPD max voltages 

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@cisco.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: <stable@vger.kernel.org>      # for v4.15
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
This commit is contained in:
Hans Verkuil 2017-12-16 05:44:13 -05:00 committed by Mauro Carvalho Chehab
parent a4a02b6ec3
commit dac15ed62d
1 changed files with 5 additions and 1 deletions
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Documentation/devicetree/bindings/media/cec-gpio.txt
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@ -4,6 +4,10 @@ The HDMI CEC GPIO module supports CEC implementations where the CEC line
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>