Hi Laurent, Thank you for your feedback! > From: devicetree-owner@xxxxxxxxxxxxxxx <devicetree-owner@xxxxxxxxxxxxxxx> On Behalf Of Laurent Pinchart > Sent: 07 November 2019 18:01 > Subject: Re: [PATCH v3 1/8] dt-bindings: display: Add bindings for LVDS bus-timings > > Hello Fabrizio, > > On Thu, Aug 29, 2019 at 02:38:06PM +0000, Fabrizio Castro wrote: > > On 29 August 2019 15:03 Rob Herring wrote: > > > On Wed, Aug 28, 2019 at 1:36 PM Fabrizio Castro wrote: > > >> > > >> Dual-LVDS connections need markers in the DT, this patch adds > > >> some common documentation to be referenced by both panels and > > >> bridges. > > >> > > >> Signed-off-by: Fabrizio Castro <fabrizio.castro@xxxxxxxxxxxxxx> > > >> > > >> --- > > >> v2->v3: > > >> * new patch > > >> --- > > >> .../bindings/display/bus-timings/lvds.yaml | 38 ++++++++++++++++++++++ > > >> 1 file changed, 38 insertions(+) > > >> create mode 100644 Documentation/devicetree/bindings/display/bus-timings/lvds.yaml > > >> > > >> diff --git a/Documentation/devicetree/bindings/display/bus-timings/lvds.yaml > b/Documentation/devicetree/bindings/display/bus-timings/lvds.yaml > > >> new file mode 100644 > > >> index 0000000..f35b55a > > >> --- /dev/null > > >> +++ b/Documentation/devicetree/bindings/display/bus-timings/lvds.yaml > > >> @@ -0,0 +1,38 @@ > > >> +# SPDX-License-Identifier: GPL-2.0 > > > > > > (GPL-2.0-only OR BSD-2-Clause) is preferred for new bindings. > > > > > >> +%YAML 1.2 > > >> +--- > > >> +$id: http://devicetree.org/schemas/display/bus-timings/lvds.yaml# > > >> +$schema: http://devicetree.org/meta-schemas/core.yaml# > > >> + > > >> +title: Common Properties for bus timings of LVDS interfaces > > >> + > > >> +maintainers: > > >> + - Thierry Reding <thierry.reding@xxxxxxxxx> > > >> + - Fabrizio Castro <fabrizio.castro@xxxxxxxxxxxxxx> > > >> + > > >> +description: | > > >> + This document defines device tree properties common to LVDS and dual-LVDS > > >> + interfaces, where a dual-LVDS interface is a dual-link connection with even > > >> + pixels traveling on one connection, and with odd pixels traveling on the other > > >> + connection. > > As you define a dual-LVDS interface as "a dual-link connection", should > this be "even pixels traveling on one link, and with odd pixels > traveling on the other link" ? Will change. Thanks, Fab > > > >> + This document doesn't constitue a device tree binding specification by itself > > > > > > typo: constitute > > > > Well spotted! > > > > >> + but is meant to be referenced by device tree bindings. > > >> + When referenced from panel or bridge device tree bindings, the properties > > >> + defined in this document are defined as follows. The panel and bridge device > > >> + tree bindings are responsible for defining whether each property is required > > >> + or optional. > > >> + > > >> +properties: > > >> + dual-lvds-even-pixels: > > >> + type: boolean > > >> + description: > > >> + This property is specific to an input port of a sink device. When > > > > > > The schema should define what nodes these go in. The description seems > > > to indicate in 'port' nodes (or endpoint?), but your use in the panel > > > binding puts them in the parent. > > > > Did you manage to read this? > > https://patchwork.kernel.org/cover/11119607/ > > > > Could you please advice on how to do this properly? > > > > >> + specified, it marks the port as recipient of even-pixels. > > >> + > > >> + dual-lvds-odd-pixels: > > >> + type: boolean > > >> + description: > > >> + This property is specific to an input port of a sink device. When > > >> + specified, it marks the port as recipient of odd-pixels. > > > > > > However, I don't think you even need these. A panel's port numbers are > > > fixed can imply even or odd. For example port@0 can be even and port@1 > > > can be odd. The port numbering is typically panel specific, but we may > > > be able to define the numbering generically if we don't already have > > > panels with multiple ports. > > > > > > Also, aren't there dual link DSI panels? > > > > This is the result of a discussion on here: > > https://patchwork.kernel.org/patch/11095547/ > > > > Have you come across it? > > Let me repeat my comments from that thread for Rob in order to > centralize the discussion here. > > > Taking one step back to look at the big picture, what we need is for the > > source to know what pixel (odd or even) to send on each LVDS output. For > > that it needs to know what pixel is expected by the sink the the inputs > > connected to the source's outputs. From each source output we can easily > > locate the DT nodes corresponding to the connected sink's input ports, > > but that doesn't give us enough information. From there, we could > > > > - Infer the odd/even pixel expected by the source based on the port > > numbers. This would require common DT bindings for all dual-link LVDS > > sinks that specify the port ordering (for instance the bindings could > > mandate that lowest numbered port correspond to even pixels). > > > > - Read the odd/even pixel expected by the source from an explicit DT > > property, as proposed above. This would also require common DT > > bindings for all dual-link LVDS sinks that define these new > > properties. This would I think be better than implicitly infering it > > from DT port numbers. > > > > - Retrieve the information from the sink drm_bridge at runtime. This > > would require a way to query the bridge for the mapping from port > > number to odd/even pixel. The DRM_LINK_DUAL_LVDS_ODD_EVEN flag could > > be used for that, and would then be defined as "the lowest numbered > > port corresponds to odd pixels and the highest numbered port > > corresponds to even pixels". > > > > The second and third options would both work I think. The third one is > > roughly what you've implemented, except that I think the flag > > description should be clarified. > > Rob, what's your opinion ? We could certainly, in the context of a > panel, decide of a fixed mapping of port numbers to odd/even pixels, but > the issue is that sources need to know which pixels to send on which > link (assuming of course that this can be configured on the source > side). We thus need a way for the source to answer, at runtime, the > question "which of ports A and B of the sink correspond to even and odd > pixels ?". This can't be inferred by the source from the sink port > numbers, as the mapping between port number and odd/even pixels is > specific to each sink. We thus need to either store that property in the > DT node of the sink (option 2) or query it at runtime from the sink > (option 3). > > I like option 2 as it's more explicit, but option 3 minimizes the > required properties in DT, which is always good. Patch 3/8 introduces a > helper that abstracts this from a sink point of view (which I think is a > very good idea), so once we decide which option to use, only 3/8 may > need to be adapted, the other patches should hopefully not require > rework. > > -- > Regards, > > Laurent Pinchart _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
