Hi Rob, Ping ? On Monday 17 Oct 2016 15:42:56 Laurent Pinchart wrote: > On Friday 14 Oct 2016 07:40:14 Rob Herring wrote: > > On Sun, Oct 9, 2016 at 11:33 AM, Laurent Pinchart wrote: > >> On Saturday 08 Oct 2016 20:29:39 Rob Herring wrote: > >>> On Tue, Oct 04, 2016 at 07:23:29PM +0300, Laurent Pinchart wrote: > >>>> LVDS is a physical layer specification defined in ANSI/TIA/EIA-644-A. > >>>> Multiple incompatible data link layers have been used over time to > >>>> transmit image data to LVDS panels. This binding supports display > >>>> panels compatible with the JEIDA-59-1999, Open-LDI and VESA SWPG > >>>> specifications. > >>>> > >>>> Signed-off-by: Laurent Pinchart > >>>> <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx> > >>>> --- > >>>> > >>>> .../bindings/display/panel/panel-lvds.txt | 119 ++++++++++++ > >>>> 1 file changed, 119 insertions(+) > >>>> create mode 100644 > >>>> Documentation/devicetree/bindings/display/panel/panel-lvds.txt> > >>>> > >>>> diff --git > >>>> a/Documentation/devicetree/bindings/display/panel/panel-lvds.txt > >>>> b/Documentation/devicetree/bindings/display/panel/panel-lvds.txt > >>>> new file mode 100644 > >>>> index 000000000000..250861f2673e > >>>> --- /dev/null > >>>> +++ b/Documentation/devicetree/bindings/display/panel/panel-lvds.txt > >>>> @@ -0,0 +1,119 @@ > >>>> +Generic LVDS Panel > >>>> +================== > >>>> + > >>>> +LVDS is a physical layer specification defined in ANSI/TIA/EIA-644-A. > >>>> Multiple > >>>> +incompatible data link layers have been used over time to transmit > >>>> image data > >>>> +to LVDS panels. This bindings supports display panels compatible with > >>>> the > >>>> +following specifications. > >>>> + > >>>> +[JEIDA] "Digital Interface Standards for Monitor", JEIDA-59-1999, > >>>> February > >>>> +1999 (Version 1.0), Japan Electronic Industry Development Association > >>>> (JEIDA) > >>>> +[LDI] "Open LVDS Display Interface", May 1999 (Version 0.95), > >>>> National > >>>> +Semiconductor > >>>> +[VESA] "VESA Notebook Panel Standard", October 2007 (Version 1.0), > >>>> Video > >>>> +Electronics Standards Association (VESA) > >>>> + > >>>> +Device compatible with those specifications have been marketed under > >>>> the > >>>> +FPD-Link and FlatLink brands. > >>>> + > >>>> + > >>>> +Required properties: > >>>> +- compatible: shall contain "panel-lvds" > >>> > >>> Maybe as a fallback, but on its own, no way. > >> > >> Which brings an interesting question: when designing generic DT > >> bindings, what's the rule regarding > > Looks like I forgot part of the question. I meant to ask what is the rule > regarding usage of more precise compatible strings ? > > For instance (but perhaps not the best example), the > input/rotary-encoder.txt bindings define a "rotary-encoder" compatible > string, with no other bindings defining more precise compatible strings for > the exact rotary encoder model. When it comes to panels I believe it makes > sense to define model-specific compatible strings even if they're unused by > drivers. I'm however wondering what the rule is there, and where those > device-specific compatible strings should be defined. I'd like to avoid > using one file per panel model as done today for the simple-panel bindings. > > > Call it "simple" so I can easily NAK it. :) > > > > Define a generic structure, not a single binding trying to serve all. > > > >>> > +- width-mm: panel display width in millimeters > >>> > +- height-mm: panel display height in millimeters > >>> > >>> This is already documented for all panels IIRC. > >> > >> Note that this DT binding has nothing to do with the simple-panel > >> binding. It is instead similar to the panel-dpi and panel-dsi-cm bindings > >> (which currently don't but should specify the panel size in DT). The LVDS > >> panel driver will *not* include any panel-specific information such as > >> size or timings, these are specified in DT. > > > > The panel bindings aren't really different. The biggest difference was > > location in the tree, but we now generally allow panels to be either a > > child of the LCD controller or connected with OF graph. We probably > > need to work on restructuring the panel bindings a bit. We should have > > an inheritance with a base panel binding of things like size, label, > > graph, backlight, etc, then perhaps an interface specific bindings for > > LVDS, DSI, and parallel, then a panel specific binding. With this the > > panel specific binding is typically just a compatible string and which > > inherited properties apply to it. > > That sounds good to me, but we have multiple models for panel bindings. > > As you mentioned panels can be referenced through an LCD controller node > property containing a phandle to the panel node, or through OF graph. That's > a situation we have today, and we need to keep supporting both (at least > for existing panels, perhaps not for the new ones). > > Another difference is how to express panel data such as size and timings. > The simple-panel DT bindings don't contain such data and expects the > drivers to contain a table of panel data for all models supported, while > the DPI, DSI and now the proposed LVDS panel bindings contain properties > for panel data. > > How would you like to reconcile all that ? > > >>>> +- data-mapping: the color signals mapping order, "jeida-18", > >>>> "jeida-24" > >>>> + or "vesa-24" > >>> > >>> Maybe this should be part of the compatible. > >> > >> I've thought about it, but given that some panels support selecting > >> between multiple modes (through a mode pin that is usually hardwired), I > >> believe a separate DT property makes sense. > > > > Okay. > > > >> Furthermore, LVDS data organization is controlled by the combination of > >> both data-mapping and data-mirror. It makes little sense from my point > >> of view to handle one as part of the compatible string and the other one > >> as a separate property. > >> > >>> > +Optional properties: > >>> > +- label: a symbolic name for the panel > >>> > >>> Could be for any panel or display connector. > >> > >> Yes, but I'm not sure to understand how that's relevant :-) > > > > Meaning it should be a common property. > > Sure. So you expect me to reorganize all the panels and connectors DT > bindings in order to get this one merged ? :-) > > >>>> +- avdd-supply: reference to the regulator that powers the panel > >>>> analog supply > >>>> +- dvdd-supply: reference to the regulator that powers the panel > >>>> digital supply > >>> > >>> Which one has to be powered on first, what voltage, and with what time > >>> in between? This is why "generic" or "simple" bindings don't work. > >> > >> The above-mentioned specifications also define connectors, pinouts and > >> power supplies, but many LVDS panels compatible with the LVDS physical > >> and data layers use a different connector with small differences in > >> power > >> supplies. > >> > >> I believe the voltage is irrelevant here, it doesn't need to be > >> controlled by the operating system. Power supplies order and timing is > >> relevant, I'll investigate the level of differences between panels. I'm > >> also fine with dropping those properties for now. > > > > Whether you have control of the supplies is dependent on the board. > > Dropping them is just puts us in the simple binding trap. The simple > > bindings start out that way and then people keep adding to them. > > Damn, you can't be fooled easily ;-) > > On a more serious note, I'd like to design the bindings in a way that > wouldn't require adding device-specific code in the driver for each panel > model, given that in most cases power supply handling will be generic. > What's your opinion about a generic power supply model that would be used > in the default case, with the option to override it with device-specific > code when needed ? > > >>>> +- data-mirror: if set, reverse the bit order on all data lanes (6 to > >>>> 0 instead > >>>> + of 0 to 6) > > > > On this one, make the name describe the order. "mirror" requires that > > I know what is normal ordering. Perhaps "data-msb-first". > > Sounds good to me, I'll use that. -- Regards, Laurent Pinchart
