Hi Rob, On Wed, 2017-04-19 at 17:09 -0500, Rob Herring wrote: > On Thu, Apr 13, 2017 at 05:48:11PM +0200, Philipp Zabel wrote: > > This adds device tree binding documentation for mmio-based syscon > > multiplexers controlled by a single bitfield in a syscon register > > range. > > > > Signed-off-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> > > --- > > Documentation/devicetree/bindings/mux/mmio-mux.txt | 56 ++++++++++++++++++++++ > > 1 file changed, 56 insertions(+) > > create mode 100644 Documentation/devicetree/bindings/mux/mmio-mux.txt > > > > diff --git a/Documentation/devicetree/bindings/mux/mmio-mux.txt b/Documentation/devicetree/bindings/mux/mmio-mux.txt > > new file mode 100644 > > index 0000000000000..11d96f5d98583 > > --- /dev/null > > +++ b/Documentation/devicetree/bindings/mux/mmio-mux.txt > > @@ -0,0 +1,56 @@ > > +MMIO bitfield-based multiplexer controller bindings > > + > > +Define a syscon bitfield to be used to control a multiplexer. The parent > > +device tree node must be a syscon node to provide register access. > > + > > +Required properties: > > +- compatible : "gpio-mux" > > ? > > > +- reg : register base of the register containing the control bitfield > > +- bit-mask : bitmask of the control bitfield in the control register > > +- bit-shift : bit offset of the control bitfield in the control register > > +- #mux-control-cells : <0> > > +* Standard mux-controller bindings as decribed in mux-controller.txt > > + > > +Optional properties: > > +- idle-state : if present, the state the mux will have when idle. The > > + special state MUX_IDLE_AS_IS is the default. > > + > > +The multiplexer state is defined as the value of the bitfield described > > +by the reg, bit-mask, and bit-shift properties, accessed through the parent > > +syscon. > > + > > +Example: > > + > > + syscon { > > + compatible = "syscon"; > > + > > + mux: mux-controller@3 { > > + compatible = "mmio-mux"; > > + reg = <0x3>; > > + bit-mask = <0x1>; > > + bit-shift = <5>; > > This pattern doesn't scale once you have multiple fields @ addr 3. I > also don't really think a node per register field in DT really scales. Thanks, I have been a bit uneasy with the separate per-bitfield mux controller node, so I'm eager to agree. But thit makes me unsure how to best represent the information that is spelled out above. > I think the parent should be declared as a mux controller instead. The syscon node itself should be the mux controller? Would you expect the mmio-mux driver bind to the syscon node, or should the mux framework handle creation of the mux controls in this case (i.e. does the syscon node get a "mmio-mux" added to its compatible list)? > You could encode the mux addr and bit position in the mux cells. What about the bit-mask / bitfield width? Just add a cell for it? gpr: syscon { compatible = "mmio-mux", "syscon", "simple-mfd"; #mux-control-cells = <3>; video-mux { compatible = "video-mux"; /* register 0x3, bits [6:5] */ mux-controls = <&gpr 0x3 5 0x3>; ports { /* ports 0..5 */ }; }; }; Or maybe using MSB and LSB would be better to read? video-mux { /* register 0x3, bits [6:5] */ mux-control = <&gpr 0x3 6 5>; ports { /* ports 0..5 */ }; }; > > + #mux-control-cells = <0>; > > + }; > > + }; > > + > > + video-mux { > > + compatible = "video-mux"; > > + mux-controls = <&mux>; > > The mux binding was largely defined for a single control controling > multiple muxes. This doesn't really fit that, but I guess this is an > improvement over a custom syscon phandle. What I especially like about the mux-controls property is that would allow me to use the gpio-mux driver (or any other mux controller) instead of having to code variants of the video-mux for all possible control schemes. regards Philipp -- 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