On Thu, Oct 27, 2016 at 12:17:24AM +0200, Maxime Ripard wrote:

Hi Rob,

On Wed, Oct 26, 2016 at 05:13:46PM -0500, Rob Herring wrote:

quoted

On Thu, Oct 20, 2016 at 11:43:37AM +0800, Chen-Yu Tsai wrote:

quoted

Some rgb-to-vga bridges have an enable GPIO, either directly tied to
an enable pin on the bridge IC, or indirectly controlling a power
switch.

Add support for it.

Signed-off-by: Chen-Yu Tsai <redacted>
---
 .../bindings/display/bridge/dumb-vga-dac.txt       |  2 ++
 drivers/gpu/drm/bridge/dumb-vga-dac.c              | 28 ++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/Documentation/devicetree/bindings/display/bridge/dumb-vga-dac.txt b/Documentation/devicetree/bindings/display/bridge/dumb-vga-dac.txt
index 003bc246a270..d3484822bf77 100644
--- a/Documentation/devicetree/bindings/display/bridge/dumb-vga-dac.txt
+++ b/Documentation/devicetree/bindings/display/bridge/dumb-vga-dac.txt

@@ -16,6 +16,8 @@ graph bindings specified in Documentation/devicetree/bindings/graph.txt.
 - Video port 0 for RGB input
 - Video port 1 for VGA output
 
+Optional properties:
+- enable-gpios: GPIO pin to enable or disable the bridge

This should also define the active state.

quoted

+static void dumb_vga_enable(struct drm_bridge *bridge)
+{
+	struct dumb_vga *vga = drm_bridge_to_dumb_vga(bridge);
+
+	if (vga->enable_gpio)
+		gpiod_set_value_cansleep(vga->enable_gpio, 1);

So the driver should allow either active high or low.

You mean like having a enable-active-high property? Isn't that
redundant with the GPIO flags?

Correct - the gpiod APIs remove the need for drivers to know the
polarity of the signal, handling it inside the GPIO subsystem
instead, controlled either from the gpiod lookup tables in legacy
board files, or the DT specification for the GPIO.

So, in drivers, gpiod_set_value*(, 1) means "set gpio to active
level" and gpiod_set_value*(, 0) means "set gpio to inactive level".

Far nicer than all the bugs we've had with the legacy GPIO interfaces
with random different drivers implementing random different ways to
invert the signal, with all the pain that brings with it when a
platform comes along with a different inversion state.

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