Hi, Stephen 2013/8/31 Stephen Warren <swarren@xxxxxxxxxxxxx>: > On 08/26/2013 06:50 PM, wangyuhang wrote: >> Add spi-tmax-nbits and spi-rmax-nbits for spi slave node. >> Modify the related dt document(spi-bus.txt) >> spi-tmax-nbits:Max number of bits slave will use for MOSI(writting) >> spi-rmax-nbits:Max number of bits slave will use for MISO(reading) >> Support for spi-tx/rmax-nbits in SPI framework has been picked[1]. >> [1]: http://comments.gmane.org/gmane.linux.kernel.spi.devel/14420 >> Commit Id:f477b7fb13df2b843997559ff34e87d054ba6538 > >> diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt > >> +- spi-tmax-nbits - (optional) Max number of bits slave will use for >> + MOSI(writting) >> +- spi-rmax-nbits - (optional) Max number of bits slave will use for >> + MISO(reading) > > I would suggest the property names > > spi-tx-num-wires, spi-rx-num-wires > > or: > > spi-tx-bus-width, spi-rx-bus-width (this option from Tomasz Figa on IRC) > > Those name alone self-document their purpose much more clearly to me. > > I would also change the descriptions a bit, resulting in the following > overall: > > ========== > - spi-tx-num-wires - (optional) The number of data wires that > transfer data from the SPI controller to the > SPI device. Defaults to 1 if not present. > - spi-rx-num-wires - (optional) The number of data wires that > transfer data from the SPI device to the > SPI controller. Defaults to 1 if not present. > ========== > OK, that seems better. >> +So if for example the slave has 4 wires for writting and 2 wires for reading, >> +and the spi-tx/rx-nbits property should be set as follows: >> + >> +spi-tmax-nbits = <4>; >> +spi-rmax-nbits = <2>; >> + >> +Now the value that spi-tmax-nbits and spi-rmax-nbits can receive is only >> +1(single), 2(dual) and 4(quad). If you don't set spi-tmax-nbits or spi-rmax-nbits, >> +spi_device mode will be set in single(1 wire) as default. Another point, if >> +property:spi-3wire is set, spi-t/rmax-nbits is forbidden to set to <2 or 4>, >> +otherwise, an errro will return. > > I think most of that explanation can be removed if you use the text I > wrote above. > > I'm not sure you should ban spi-3wire if those properties are specified; > can't all those properties be present together, if the num-wires are set > to 1? Actually, isn't spi-3write the default; what does that property mean? Property spi-3write means some controllers only have cs, clk and sda(SI/SO shared) 3 wires. So if spi-3wire is set, then dual and quad set should be forbidden. I didn't mean that spi-3wire can't be present together with spi-tx/rx-num-wires, if set to <1> it's OK. Just can't be <2 | 4>(dual and quad). -- 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
