linux-kernel - Re: [RFC net-next 00/15] net: A socket API for LoRa

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Message-ID: <f1967750-0a42-0e76-2d7d-da293bc351af@suse.de>
Date:   Thu, 9 Aug 2018 02:50:39 +0200
From:   Andreas Färber <afaerber@...e.de>
To:     Jian-Hong Pan <starnight@...cu.edu.tw>
Cc:     netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Jiri Pirko <jiri@...nulli.us>,
        Marcel Holtmann <marcel@...tmann.org>,
        "David S. Miller" <davem@...emloft.net>,
        Matthias Brugger <mbrugger@...e.com>,
        Janus Piwek <jpiwek@...oweurope.com>,
        Michael Röder <michael.roeder@...et.eu>,
        Dollar Chen <dollar.chen@...ec.com>,
        Ken Yu <ken.yu@...wireless.com>,
        Konstantin Böhm <konstantin.boehm@...ud.de>,
        Jan Jongboom <jan.jongboom@....com>,
        Jon Ortego <Jon.Ortego@...t.de>, contact@...otlab.com,
        Ben Whitten <ben.whitten@...rdtech.com>,
        Brian Ray <brian.ray@...k-labs.com>, lora@...balsat.com.tw,
        Alexander Graf <agraf@...e.de>,
        Michal Kubeček <mkubecek@...e.cz>,
        Rob Herring <robh@...nel.org>, devicetree@...r.kernel.org,
        Steve deRosier <derosier@...il.com>,
        Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
        Pieter Robyns <pieter.robyns@...sselt.be>,
        Hasnain Virk <Hasnain.Virk@....com>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        linux-wpan <linux-wpan@...r.kernel.org>,
        Stefan Schmidt <stefan@...enfreihafen.org>,
        Daniele Comel <dcomel@...ot.com>,
        Xue Liu <liuxuenetmail@...il.com>,
        Sebastian Heß <shess@...sware.de>
Subject: Re: [RFC net-next 00/15] net: A socket API for LoRa

Am 05.08.2018 um 02:11 schrieb Andreas Färber:
> Am 03.07.2018 um 17:11 schrieb Jian-Hong Pan:
>> 2018-07-01 19:07 GMT+08:00 Andreas Färber <afaerber@...e.de>:
>>> 5) Many of the modules support multiple modes, such as LoRa, LoRaWAN and FSK.
>>>    Lacking a LoRaWAN implementation, I am currently switching them into LoRa
>>>    mode at probe time wherever possible. How do we deal with that properly?
[...]
> Independently of what LoRaWAN does, the
> user needs to be able to send on the physical layer from a selection of
> LoRa, GFSK, FSK, OOK, GMSK and MSK.
> Supposedly Wireless M-Bus and IEEE 802.15.4 can be implemented via those
> according to the SX1276 datasheet.
> 
> This opens a can of worms...
> 
> SX127x has a single channel, so I don't think there should be six
> network interfaces lora0, gfsk0, fsk0, ook0, gmsk0 and msk0 exposed to
> the user.
> Having a lora0 interface speak non-LoRa modulations may be confusing,
> but since the chip is sold as LoRa transceiver it might be acceptable.
> 
> SX130x has 8+2 channels, with IF9 dedicated to GFSK/FSK. It appears to
> use one FIFO for receiving (up to 16 packets) and can only transmit one
> packet at a time. So I think this should be one lora0 interface, too.
> 
> With a view to supporting non-LoRa RF chipsets such as Si4xxx (GFSK,
> FSK, OOK) or nRF905 and nRF24L01+ (both GFSK) at a later date, I don't
> think those modulations should be some netlink option on a PF_LORA
> interface but cleanly distinguished as ETH_P_GFSK or something.
> For example, the Chistera Pi HAT has both an RFM95W and an RFM22 module.

Answering myself here: MSK is a special case of FSK, and GMSK a special
case of GFSK. SX1276 allows to switch between LoRa and FSK/OOK modes,
and in FSK/OOK mode between FSK and OOK modulation types and for FSK
modulation allows to set Gaussian filter values. I assume (G)MSK is
selected indirectly through BitRate and Fdev settings or something.

So we would just need ETH_P_FSK and ETH_P_OOK plus some skb fields for
ETH_P_FSK.

Regards,
Andreas

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