Hi Archit, On Friday 07 Oct 2016 10:27:31 Archit Taneja wrote: > On 10/07/2016 02:34 AM, Laurent Pinchart wrote: > > 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.t > >>>>>>> xt > >>>>>>> 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, I'm testing the patch with rcar-du-drm and will provide results today. > and change the compatible to "dumb-vga-dac". Feel free to ignore the bikeshedding, but "transparent" could be a candidate to replace "dumb" (either as "vga-dac-transparent" or "transparent-vga-dac"). -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
