Hi Rob, On Mon, May 16, 2016 at 09:07:18AM -0500, Rob Herring wrote: > On Mon, May 16, 2016 at 7:47 AM, Maxime Ripard > <maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote: > > Some boards have an entirely passive RGB to VGA bridge, based on either > > DACs or resistor ladders. > > > > Those might or might not have an i2c bus routed to the VGA connector in > > order to access the screen EDIDs. > > > > Add a bridge that doesn't do anything but expose the modes available on the > > screen, either based on the EDIDs if available, or based on the XGA > > standards. > > > > Signed-off-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx> > > --- > > .../bindings/display/bridge/dumb-vga.txt | 40 +++++ > > drivers/gpu/drm/bridge/Kconfig | 6 + > > drivers/gpu/drm/bridge/Makefile | 1 + > > drivers/gpu/drm/bridge/dumb-vga.c | 186 +++++++++++++++++++++ > > 4 files changed, 233 insertions(+) > > create mode 100644 Documentation/devicetree/bindings/display/bridge/dumb-vga.txt > > create mode 100644 drivers/gpu/drm/bridge/dumb-vga.c > > > > diff --git a/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt > > new file mode 100644 > > index 000000000000..757f04de97f3 > > --- /dev/null > > +++ b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt > > @@ -0,0 +1,40 @@ > > +Passive RGB to VGA bridge > > +------------------------- > > + > > +This binding is aimed for entirely passive RGB to VGA bridges that do not > > +require any configuration. > > No reset or enable lines or regulators? On the three designs I've seen: - One doesn't need any of these - One has a GPIO enable pin but with it's resistor not populated - One has a regulator controlled by a GPIO So I guess in most cases, we don't need anything, but we still might to cover all cases. > > + > > +Required properties: > > + > > +- compatible: Should be "dumb-vga-bridge" > > + > > +Optional properties: > > + > > +- ddc-i2c-bus: phandle to the i2c bus used to communicate with the monitor > > The i2c bus is a property of the connector, not the bridge chip, so it > belongs in a VGA connector node (which we already have binding for). > > I think for the really "dumb" (or transparent case), you should only > have a connector. For anything more complex, then you should have both > a DAC and connector node. So, in essence, something like: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/r8a7794-alt.dts#n37 > On the driver side, I think we could handle multiple connectors with a > single driver. Ideally, that would work with any DRM driver that has a > connector node. I'm not sure what you mean by that. I really think it should be a separate driver in order to share the common code that so far the current implementations put in some driver specific code (even though it might be completely generic). Thanks! Maxime -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com
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