On Mon, Jan 15, 2024 at 07:02:55PM +0100, Krzysztof Kozlowski wrote: > On 15/01/2024 18:36, Christoph Winklhofer wrote: > > On Sun, Jan 14, 2024 at 04:55:42PM +0100, Krzysztof Kozlowski wrote: > >> On 14/01/2024 15:47, Christoph Winklhofer wrote: > >>> On Sun, Jan 14, 2024 at 11:54:48AM +0100, Krzysztof Kozlowski wrote: > >>>> On 13/01/2024 19:04, Christoph Winklhofer wrote: > >>>>> On Fri, Jan 12, 2024 at 07:39:17PM -0600, Rob Herring wrote: > >>>>>> On Sat, Jan 06, 2024 at 05:02:24PM +0100, Christoph Winklhofer wrote: > >>>>>>> Add device tree binding for UART 1-Wire bus. > >>>>>>> > >>>>>>> Signed-off-by: Christoph Winklhofer <cj.winklhofer@xxxxxxxxx> > >>>>>>> --- > >>>>>>> Documentation/devicetree/bindings/w1/w1-uart.yaml | 62 +++++++++++++++++++++++ > >>>>>>> 1 file changed, 62 insertions(+) > >>>>>>> > >>>>>>> diff --git a/Documentation/devicetree/bindings/w1/w1-uart.yaml b/Documentation/devicetree/bindings/w1/w1-uart.yaml > >>>>>>> new file mode 100644 > >>>>>>> index 000000000000..6b90693b2ca0 > >>>>>>> --- /dev/null > >>>>>>> +++ b/Documentation/devicetree/bindings/w1/w1-uart.yaml > >>>>>>> @@ -0,0 +1,62 @@ > >>>>>>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause > >>>>>>> +%YAML 1.2 > >>>>>>> +--- > >>>>>>> +$id: http://devicetree.org/schemas/w1/w1-uart.yaml# > >>>>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml# > >>>>> ... > >>>>>>> +properties: > >>>>>>> + compatible: > >>>>>>> + const: w1-uart > >>>>>>> + > >>>>>>> + reset-speed: > >>>>>>> + $ref: /schemas/types.yaml#/definitions/uint32 > >>>>>>> + default: 9600 > >>>>>>> + description: | > >>>>>> > >>>>>> Don't need '|' if no formatting > >>>>>> > >>>>> > >>>>> Ok. > >>>>> > >>>>>>> + The baud rate for the 1-Wire reset and presence detect. > >>>>>>> + > >>>>>>> + touch_0-speed: > >>>>>> > >>>>>> Don't use '_' in property names. > >>>>>> > >>>>>> I'm somewhat familar with 1-wire, but I don't get what 'touch' means > >>>>>> here. I assume these are low and high times which are a function of the > >>>>>> baudrate. > >>>>>> > >>>>> > >>>>> I change the name to 'write-0-speed' and 'write-1-speed'. The function > >>>>> in the w1-framework is named 'touch_bit' - therefore the previous > >>>>> naming. > >>>>> > >>>>> It is the baud-rate used in the 1-Wire cycle to write a 0-Bit > >>>>> (write-0-speed) and to perform a 1-Wire cycle that writes a 1-Bit and > >>>>> reads a 0-Bit or 1-Bit (write-1-speed). > >>>> > >>>> > >>>> Then probably -bps: > >>>> https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/property-units.yaml > >>> > >>> The serial.yaml uses prefix -speed for the baud rate but I can change it > >>> to -bps. > >> > >> Do you reference serial.yaml? > >> > > > > No, serial.yaml is not referenced but 'onewire' will be a child-node of > > a serial-device which already defines baud rate related properties > > with -speed (e.g. max-speed although not used in w1-uart). Hence, I > > thought -speed is typically used for baud rates. > > Ah, it defines max-speed for childre, so for onewire. Re-using that > property would make sense, but since you are defining completely new > properties, let's use proper (-bps) naming. > Ok. > I still wonder, why would you use different baud rates for these three > different operations? The timing for the pulse on the 1-Wire bus, to perform a 1-Wire reset or read/write is too different to use the same baud rate for them. The pulse can only be generated with the transmission of a single byte (to initiate the operation and to evaluate the response), since every UART packet starts low and ends high, only a limited set of baud rates are possible. Read-0/1 and Write-1 have the same low-time and therefore share the same baud rate setting, actually this baud could be higher. Otherwise, for Write-0 the maximum baud-rate is somewhere near 115200. The table lists the low-time range for the 1-Wire standard speed (overdrive is currently not implemented by the driver): Operation | Low-Time (usec) | Baud rate (default) ----------+-----------------+-------------------- Reset | 480 - 640 | 9600 Read-0/1 | 5 - 15 | 115200 Write-1 | 5 - 15 | 115200 Write-0 | 60 - 120 | 115200 I thought it makes sense to have the option to overwrite the default baud rates. Alternatively, the driver could probe a fixed set of different baud rates that are able to generate the timing patterns. Initially, the driver always used 9600 and 115200 - however some UART devices may not support these bauds. Now the driver requests a baud rate and checks if it can create the timing pattern with the returned one. Kind regards, Christoph
