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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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6
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 is hooked up to a pull-up GPIO line and - optionally - the HPD line is
hooked up to another GPIO line. 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: Required properties:
- compatible: value must be "cec-gpio". - compatible: value must be "cec-gpio".
- cec-gpios: gpio that the CEC line is connected to. The line should be - 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 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 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> #include <dt-bindings/gpio/gpio.h>