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The Raspberry Pi 3 GPIO expander is controlled by the VC4 firmware over
I2C. The firmware mailbox interface allows the ARM core to control the
GPIO lines.
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>