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