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Date:   Mon, 11 May 2020 09:24:09 -0700
From:   Stephen Boyd <>
To:     Douglas Anderson <>,,,,,,,,,
Cc:,,,,,,,,, Douglas Anderson <>,
Subject: Re: [PATCH v5 1/6] drm/bridge: ti-sn65dsi86: Export bridge GPIOs to Linux

Quoting Douglas Anderson (2020-05-07 14:34:55)
> The ti-sn65dsi86 MIPI DSI to eDP bridge chip has 4 pins on it that can
> be used as GPIOs in a system.  Each pin can be configured as input,
> output, or a special function for the bridge chip.  These are:
> - GPIO1: SUSPEND Input
> - GPIO4: PWM
> Let's expose these pins as GPIOs.  A few notes:
> - Access to ti-sn65dsi86 is via i2c so we set "can_sleep".
> - These pins can't be configured for IRQ.
> - There are no programmable pulls or other fancy features.
> - Keeping the bridge chip powered might be expensive.  The driver is
>   setup such that if all used GPIOs are only inputs we'll power the
>   bridge chip on just long enough to read the GPIO and then power it
>   off again.  Setting a GPIO as output will keep the bridge powered.
> - If someone releases a GPIO we'll implicitly switch it to an input so
>   we no longer need to keep the bridge powered for it.
> Because of all of the above limitations we just need to implement a
> bare-bones GPIO driver.  The device tree bindings already account for
> this device being a GPIO controller so we only need the driver changes
> for it.
> NOTE: Despite the fact that these pins are nominally muxable I don't
> believe it makes sense to expose them through the pinctrl interface as
> well as the GPIO interface.  The special functions are things that the
> bridge chip driver itself would care about and it can just configure
> the pins as needed.
> Signed-off-by: Douglas Anderson <>
> Cc: Linus Walleij <>
> Cc: Bartosz Golaszewski <>
> ---

Reviewed-by: Stephen Boyd <>

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