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Subject: Re: [RFC net-next 1/4] net: Reserve protocol identifiers for EnOcean
To:     Alexander Aring <aring@mojatatu.com>
Cc:     linux-lpwan@lists.infradead.org, linux-wpan@vger.kernel.org,
        Alexander Aring <alex.aring@gmail.com>,
        Stefan Schmidt <stefan@datenfreihafen.org>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        support@enocean.com, Jonathan Cameron <jic23@kernel.org>,
        Rob Herring <robh+dt@kernel.org>
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From:   =?UTF-8?Q?Andreas_F=c3=a4rber?= <afaerber@suse.de>
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Hi Alex,

Am 01.02.19 um 01:58 schrieb Alexander Aring:
> On Wed, Jan 30, 2019 at 02:42:29AM +0100, Andreas Färber wrote:
>> Am 29.01.19 um 13:57 schrieb Alexander Aring:
>>> On Tue, Jan 29, 2019 at 06:01:27AM +0100, Andreas Färber wrote:
>>>> EnOcean wireless technology is based on ASK (ERP1) and FSK (ERP2) modulations
>>>> for sub-GHz and on IEEE 802.15.4 for 2.4 GHz.
>>>
>>> I am not sure what you try to do here. If I see that correctly you
>>> want to add for some special protocol vendor specific transceiver which
>>> is underneath an 802.15.4 transceiver a new ARPHRD type and even more
>>> for each modulation what it supports?
>>
>> No. EnOcean uses a 4-byte node ID across PHY layers, which I am using a
>> single ARPHRD_ENOCEAN for (which you conveniently cut off above).
>>
>> As indicated above, the 868 MHz transceiver is _not_ using 802.15.4 PHY
>> or MAC to my knowledge. It does sound like you spotted "IEEE 802.15.4"
>> and literally blended out all the rest...
>>
> 
> Ah okay, I am curious about that. As far I undetstood now this has
> nothing to do with LoRa? I was not getting that point.

Correct, this is about FSK, not LoRa. The two usually come together and
I therefore need to propose a way to make also FSK usable.

> Is the PHY layer open? Do they actually refer to 802.15.4 in their
> specs, but the PHY layer is changed by... preamble, phy header, MTU?

ERP1 PHY layer appears to be ASK, ERP2 PHY layer is described as FSK.

ERP seems a MAC / Data Link protocol (ERP2 also Network layer) on top of
multiple alternative PHYs.

ASK is amplitude-modulated; FSK is frequency-modulated; 802.15.4 is PSK,
i.e. phase-modulated. Therefore from my view they are unrelated
subsystems [*].

Further, as I stated above, 802.15.4 is being used for 2.4 GHz (for
which I currently don't have any EnOcean hard-MAC transceiver), whereas
I am using FSK on 868 MHz.

The ERP layer is openly described, whereas I have not found a lot about
802.15.4 framing except for the below mentioned commands in ESP3 layer.

The EnOcean Alliance depicts ZigBee:
https://www.enocean.com/technology/radio-technology/
If that is the case, I guess we can end the 802.15.4 discussion here? ;)

No concrete documentation on how BLE is used either.

[*] With the exception that both Nemeus and ST have Sigfox DBPSK
implementations based on FSK transceivers.

>>> If it's a 802.15.4 transceiver why not using the 802.15.4 subsystem?
>>>
>>> For me it sounds more like a HardMAC transceiver driver for doing the
>>> vendor protocol. The different modulations is part of a 802.15.4 phy
>>> device class. Similar like in wireless.
>>
>> I've tried to design this exactly so that one _could_ implement it based
>> on 802.15.4 PHY framework for 2.4 GHz or based on an FSK PHY for sub-GHz
>> as a soft-MAC, layered similarly to LoRaWAN vs. LoRa, alongside the ESP
>> serdev driver in this series.
>>
>> In ESP3 the only 802.15.4 specific operations are getting/setting the
>> channel (COMMAND_2_4 packet type), and there's a CO_GET_FREQUENCY_INFO
>> command to discover frequency and protocol, with 802.15.4 having a
>> different ID than ERP2 (and I spot a value 0x30 for "Long Range" :-)).

This appears to refer to 925 MHz FSK in Japan though, not LoRa.

>> So in theory it might be possible to instantiate an 802.15.4 PHY after
>> discovering that ESP3 value, but neither is this a generic 802.15.4 PHY
>> nor a generic FSK PHY, and none of that relates to above ARPHRD really.
>>
> 
> I keep it in mind, thanks.
> 
>> PF_PACKET with SOCK_DGRAM for ETH_P_ERP2 gives me the subtelegram
>> contents to transmit via ESP, whereas SOCK_RAW would give the full frame
>> to transmit via FSK PHY. By avoiding a custom PF_ENOCEAN we seem to lose
>> the ability to prepend any protocol headers on the skb for SOCK_DGRAM.
>>
> 
> I am not quite following here. SOCK_RAW full frame and SOCK_DGRAM
> payload sounds like what I suppose it should work.
> 
> A switch of protocol will do a switch from ESP to FSK which is a phy layer
> behaviour?

No. ESP is a serial communication protocol between host and transceiver.
It abstracts the underlying radio protocol. By using SOCK_DGRAM, as
implemented in this patchset, we can pass payload data from userspace
via ESP to ERP. We cannot transmit a full SOCK_RAW ERP frame via ESP though.

My point was that by not implementing a custom PF_ERP2 protocol family
we don't have a place to implement the framing for FSK or 802.15.4
ourselves and rely on the ESP abstraction for now. Or put differently,
userspace will always need to use SOCK_DGRAM for compatibility with ESP,
and each PHY (FSK, 802.15.4, etc.) would need to re-implement framing
that payload.

>> Did you actually read my P.S. in the cover letter? I was glad to avoid
>> much PF_ socket boilerplate code here (as a playground for LoRa), and
>> now you're complaining about a single ARPHRD constant! :-/
>> By that standard we could stop implementing anything new... If you're
>> worried about number space, why has no one commented on the values added
>> for LoRa and other previous wireless technologies? No one had any such
>> comments on my LoRa RFC, nor on Jian-Hong's LoRaWAN patches, so I've
>> been reserving new ARPHRD_ constants for each technology I work on. If
>> ARPHRD_NONE would be a better value to use for PHY layers, no one
>> bothered to point it out so far! Nor did anyone suggest to Jian-Hong to
>> reuse ARPHRD_EUI64! And yet I spot nothing more suitable for EnOcean
>> addresses than a custom value. Fact is, the net_device wants some value.
>> Note that you have two ARPHRD constants assigned for 802.15.4 alone, so
>> please be fair to others.
>>
> 
> Indeed we only need one. :-)
> 
>> An 802.15.4 PHY won't help me for 868 MHz FSK - by my reading 802.15.4
>> is PSK (BPSK/OQPSK), thus incompatible with ASK/OOK and FSK/MSK.
>>
>> As noted in the cover letter, Semtech chips have FSK and OOK support
>> alongside LoRa modulation; so I am looking into FSK PHY support, both
>> for those chips as well as for some pure FSK/OOK transceivers posted to
>> linux-lpwan list (and potentially more, given time):
>> https://lists.infradead.org/pipermail/linux-lpwan/2019-January/000116.html
>> https://lists.infradead.org/pipermail/linux-lpwan/2019-January/000117.html
>> https://en.opensuse.org/User:A_faerber/LoRa_interop
>>
>> Therefore an FSK PHY's netlink interface will need to be able to handle
>> the requirements of upper-layer protocols, such as:
>> * Wireless M-Bus (which I could not yet find a suitable 868MHz hard-MAC
>> for to test against, only 169MHz; Si4432 has an Application Note AN451),
>> * KNX RF (which I have not come across a hard-MAC for either),
>> * Sigfox downstream (cf. mm002 LoRa driver as hard-MAC; no public docs),
>> * Z-Wave (not enough docs to implement much more for now), and here
>> * EnOcean Radio Protocol 2.
>>
>> In general I want to make sure my implementations can work with both
>> soft- and hard-MAC hardware out there, as demonstrated for LoRaWAN.
>> Pointing a user with hard-MAC device to a theoretical generic subsystem
>> of your preference doesn't help them, nor does it help to split the
>> community into separate hard-MAC vs. soft-MAC implementation camps that
>> make it hard for users to switch.
> 
> agree.
> 
>> * For example, when looking for how to actually use the Pine64 Z-Wave
>> adapter, back in the day I merely found an OpenHAB Raspbian(?) image
>> that as an openSUSE contributor I would surely not block my board with;
>> no explanations, no instructions, nothing. And when you have a pure Java
>> application on the one hand and a C/Python/whatever application on the
>> other, chances are that the kernel is the only common point of reuse. I
>> surely mentioned that I hate any userspace applications that attempt to
>> detect hardware on spidev/i2c-dev/tty without using the kernel-provided
>> facilities such as DT; finally, serdev allows to move any such
>> hardware-dependent tty code into the kernel - we just need to figure out
>> how to best expose functionality there (and ideally grow some more
>> helpers). Just note how patch 3/4 reuses the kernel's crc8
>> implementation instead of re-implementing it from scratch. Similarly I'd
>> love for my AT based LoRa drivers to share more serdev code, despite
>> line ending and response styles differing greatly (think
>> serdev_device_readline w/args?); binary protocols like ESP here are
>> luckily not affected as much. It could also use some more/better
>> documentation, some of the return values are wrong.
>> * As another example, we seem to be lacking a generic SDR subsystem:
>> People with SDR hardware seem to use either downstream kernel modules,
>> possibly application-generated, or closed-source userspace libraries?
>> Neither seems able to currently reuse the net subsystem for protocols.
>> And yet I've been asked repeatedly to design drivers in a way they could
>> be used with SDR, too, but without any way to actually test that today.
>> Has anyone talked to the SDR chipset/equipment vendors to remedy that?
>> The one I was in contact with simply chose not to reply again to date...
>>
>> For ETH_P_ we seem to be far away from 0xffff, so I don't see a problem
>> there? Not just was it the easiest thing to implement & test short-term,
>> but as outlined in the cover letter I saw no way here to turn that into
>> a non-net-subsystem because the data transmitted is not self-describing
>> (mostly battery-less sensors/actuators with ca. 4 byte data payload).
>> You must know that your device with id 0x12345678 conforms to profile X.
>>
>> Is describing remote devices in DT an option? (CC'ing Rob and Jonathan)
>>
>> /.../uart@foo {
>> 	enocean {
>> 		compatible = "enocean,esp3";
>> 		#address-cells = <1>;
>> 		#size-cells = <0>;
>>
>> 		window-handle@41424344 {
>> 			compatible = "manufacturer1,handle";
>> 			reg = <0x41424344>;
>> 			enocean,equipment-profile = <1 2 3>;
> 
> What are these profiles? For declaring you actually can support some
> "window-handle"?

Window handles are an example type of EnOcean sensor: Turning the handle
is used for energy harvesting to send such a short radio message, which
then needs to be interpreted as "window tilted" and not as "button 2
pressed" or "temperature is 20°C" etc.

> Can this be changed during runtime?

Someone using this patchset can obviously send any data they want and
interpret incoming data any way they want. I don't think commercial
devices do that. But then again I'm not an expert.

> Is this some kind of device class specification by EnOcean which need to
> be set into their transceiver that a management layer handle it which is
> running by firmware?

The EnOcean Alliance profiles determine the interpretation of the
payload data and status bytes.

Since none of those sensor/actuator devices are likely to run Linux, I
don't think it matters how sensors implement their MCU firmware layers.

This DT example just being a sketch, we might just encode the profile
identifier triple in the compatible string, say "enocean,a5-02-01".
The actual manufacturer and model should then not have much influence.

Each profile could be a separate kernel driver. There's 25 4BS profiles
for temperature sensors, plus 6 profiles for combinations of multiple
sensors (temperature + humidity, light + temperature + occupancy), plus
one VLD profile with three types. The first hex number in the profile
identifier (e.g., A5-02-01) is the transmitted RORG field, the others
are arbitrary identifiers to select how to read the following data bytes.

Whether such a passively read as opposed to actively polled sensor is
suitable for the iio subsystem would be for Jonathan to comment on.
Presumably such an EnOcean profile driver would have a callback that
receives the payload data and its implementation would then store the
data until it is requested via iio?

Note: It seems that wM-Bus metering payload data beyond frame formats is
even less standardized or documented than EnOcean or Z-Wave. And for
home automation there are a number of entirely proprietary/undocumented
ones based on FSK, too, which then need to go into userspace.

But again, my primary focus before Netdevconf 0x13 will be the PHY
subsystems for LoRa and FSK, not application-specific higher-level
protocols like this one, nor driver frameworks on top as discussed here.

>> 			#io-channel-cells = <1>;
>> 		};
>>
>> 		light-switch@41424348 {
>> 			compatible = "manufacturer2,rocker";
>> 			reg = <0x41424348>;
>> 			enocean,equipment-profile = <4 5 6>;
>> 			#io-channel-cells = <2>;
>> 		};
>> 	};
>> };
>>
>> Pro: This would allow to abstract sensors (iio?) and actuators (gpio?).
>>      Cf. https://patchwork.ozlabs.org/patch/1028209/ for comparison.
>> Con: How to deal with it on ACPI or on DT platforms without Overlays?
>>      How would the kernel preserve remote device state across reboots?
>>
>> So no, I don't think we can or should shoehorn non-802.15.4 PHYs into
>> your ieee802154 PHY layer. If you see ways to share code between the
>> various wireless PHYs, that would be great, but at present it seems like
>> mostly boilerplate code with nothing in your phy struct applying to FSK
>> or LoRa. Compare my cfglora series pointed to and Xue Liu's recent sysfs
>> patch under discussion. If no more comments turn up on my cfglora series
>> I'll copy it into a cfgfsk, so that I can integrate both into sx127x as
>> a base for further discussions at Netdevconf. Thanks.
>>
> 
> Share code always sounds like a good idea.

Well, if you have comments on how to go about that, such as on Xue Liu's
PHY device work, do let us know. :)

Thanks,
Andreas

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