On Fri, Oct 07, 2016 at 10:27:31AM +0530, Archit Taneja wrote: > > > On 10/07/2016 02:34 AM, Laurent Pinchart wrote: > >Hi Sean, > > > >On Thursday 06 Oct 2016 15:53:28 Sean Paul wrote: > >>On Thu, Oct 6, 2016 at 1:27 PM, Laurent Pinchart wrote: > >>>On Thursday 06 Oct 2016 17:09:57 Archit Taneja wrote: > >>>>On 10/06/2016 12:51 PM, Maxime Ripard wrote: > >>>>>On Mon, Oct 03, 2016 at 04:40:57PM +0530, Archit Taneja wrote: > >>>>>>On 09/30/2016 08:07 PM, Maxime Ripard 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. > >>>>>>> > >>>>>>>Acked-by: Rob Herring <robh@xxxxxxxxxx> > >>>>>>>Signed-off-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx> > >>>>>>>--- > >>>>>>>.../bindings/display/bridge/rgb-to-vga-bridge.txt | 48 +++++ > >>>>>>>drivers/gpu/drm/bridge/Kconfig | 7 + > >>>>>>>drivers/gpu/drm/bridge/Makefile | 1 + > >>>>>>>drivers/gpu/drm/bridge/rgb-to-vga.c | 229 +++++++++++++ > >>>>>>>4 files changed, 285 insertions(+) > >>>>>>>create mode 100644 > >>>>>>>Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.tx > >>>>>>>t > >>>>>>>create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c > >>>>>>> > >>>>>>>diff --git > >>>>>>>a/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge. > >>>>>>>txt > >>>>>>>b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge. > >>>>>>>txt > >>>>>>>new file mode 100644 > >>>>>>>index 000000000000..a8375bc1f9cb > >>>>>>>--- /dev/null > >>>>>>>+++ > >>>>>>>b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge. > >>>>>>>tx > >>>>>>>t @@ -0,0 +1,48 @@ > >>>>>>>+Dumb RGB to VGA bridge > >>>>>>>+---------------------- > >>>>>>>+ > >>>>>>>+This binding is aimed for dumb RGB to VGA bridges that do not > >>>>>>>require > >>>>>>>+any configuration. > >>>>>>>+ > >>>>>>>+Required properties: > >>>>>>>+ > >>>>>>>+- compatible: Must be "rgb-to-vga-bridge" > >>>>>> > >>>>>>I'd talked to Laurent on IRC if he's okay with this. And I guess you > >>>>>>to had discussed it during XDC too. He's suggested that it'd be better > >>>>>>to have the compatible string as "simple-vga-dac". > >>>>> > >>>>>I just wished this bikeshedding had taken place publicly and be > >>>>>actually part of that discussion, but yeah, ok. > >>>> > >>>>Sorry about that. I'd pinged him for an Ack, the discussion went > >>>>more than that :) > >>>> > >>>>>>Some of the reasons behind having this: > >>>>>> > >>>>>>- We don't need to specify "rgb" in the compatible string since most > >>>>>>simple VGA DACs can only work with an RGB input. > >>>>> > >>>>>Ok. > >>>>> > >>>>>>- Also, with "dac" specified in the string, we don't need to > >>>>>>specifically mention "bridge" in the string. Also, bridge is a drm > >>>>>>specific term. > >>>>>> > >>>>>>- "simple" is considered because it's an unconfigurable bridge, and it > >>>>>>might be misleading for other VGA DACs to not use "vga-dac". > >>>>> > >>>>>All those "simple" bindings are just the biggest lie we ever > >>>>>told. It's simple when you introduce it, and then grows into something > >>>>>much more complicated than a non-simple implementation. > >>>> > >>>>"simple" here is supposed to mean that it's an unconfigurable RGB to > >>>>VGA DAC. This isn't supposed to follow the simple-panel model, where > >>>>you add the "simple-panel" string in the compatible node, along with > >>>>you chip specific compatible string. > >>> > >>>I agree with Maxime, I don't like the word "simple". My preference would > >>>be "vga-dac" for a lack of a better qualifier than "simple" to describe > >>>the fact that the device requires no configuration. My only concern with > >>>"vga-dac" is that we would restrict usage of that compatible string for a > >>>subset of VGA DACs, with more complex devices not being compatible with > >>>"vga-dac" even though they are VGA DACs. That's a problem I can live with > >>>though. > >> > >>While we're bikeshedding (feel free to ignore my input on this), I > >>think Maxime's initial "dumb" qualifier was better than "simple". > > > >I think I agree. > > > >>I think "passive" also gets the point across better than "simple", which > >>we've already established as something else in drm. > > > >To my electrical engineer's ear, passive refers to a component or combination > >of components that is not capable of power gain. The resistors ladder VGA DAC > >that Maxime is trying to support is a passive system, but the ADV7123 VGA DAC > >that equally requires no configuration is an active component. > > If no one has any more objections within the next day, I'll pull in > Maxime's v5 RGB to VGA bridge driver, and change the compatible to > "dumb-vga-dac". That works for me. You'll probably want to update the Kconfig and file name to match though. Maxime -- Maxime Ripard, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com
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