netdev - Re: [PATCH net-next v10 1/2] net: Add a WWAN subsystem

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Date:   Tue, 13 Apr 2021 11:27:51 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Loic Poulain <loic.poulain@...aro.org>
Cc:     gregkh@...uxfoundation.org, davem@...emloft.net,
        netdev@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        bjorn.andersson@...aro.org, manivannan.sadhasivam@...aro.org,
        aleksander@...ksander.es, dcbw@...hat.com
Subject: Re: [PATCH net-next v10 1/2] net: Add a WWAN subsystem

On Mon, 12 Apr 2021 21:23:06 +0200 Loic Poulain wrote:
> This change introduces initial support for a WWAN framework. Given the
> complexity and heterogeneity of existing WWAN hardwares and interfaces,
> there is no strict definition of what a WWAN device is and how it should
> be represented. It's often a collection of multiple devices that perform
> the global WWAN feature (netdev, tty, chardev, etc).
> 
> One usual way to expose modem controls and configuration is via high
> level protocols such as the well known AT command protocol, MBIM or
> QMI. The USB modems started to expose them as character devices, and
> user daemons such as ModemManager learnt to use them.
> 
> This initial version adds the concept of WWAN port, which is a logical
> pipe to a modem control protocol. The protocols are rawly exposed to
> user via character device, allowing straigthforward support in existing
> tools (ModemManager, ofono...). The WWAN core takes care of the generic
> part, including character device management, and relies on port driver
> operations to receive/submit protocol data.
> 
> Since the different devices exposing protocols for a same WWAN hardware
> do not necessarily know about each others (e.g. two different USB
> interfaces, PCI/MHI channel devices...) and can be created/removed in
> different orders, the WWAN core ensures that all WAN ports contributing
> to the 'whole' WWAN feature are grouped under the same virtual WWAN
> device, relying on the provided parent device (e.g. mhi controller,
> USB device). It's a 'trick' I copied from Johannes's earlier WWAN
> subsystem proposal.
> 
> This initial version is purposely minimalist, it's essentially moving
> the generic part of the previously proposed mhi_wwan_ctrl driver inside
> a common WWAN framework, but the implementation is open and flexible
> enough to allow extension for further drivers.
> 
> Signed-off-by: Loic Poulain <loic.poulain@...aro.org>

> +/**
> + * enum wwan_port_type - WWAN port types
> + * @WWAN_PORT_AT: AT commands
> + * @WWAN_PORT_MBIM: Mobile Broadband Interface Model control
> + * @WWAN_PORT_QMI: Qcom modem/MSM interface for modem control
> + * @WWAN_PORT_QCDM: Qcom Modem diagnostic interface
> + * @WWAN_PORT_FIREHOSE: XML based command protocol
> + * @WWAN_PORT_MAX
> + */
> +enum wwan_port_type {
> +	WWAN_PORT_AT,
> +	WWAN_PORT_MBIM,
> +	WWAN_PORT_QMI,
> +	WWAN_PORT_QCDM,
> +	WWAN_PORT_FIREHOSE,
> +	WWAN_PORT_MAX,
> +};

include/linux/wwan.h:28: warning: Enum value 'WWAN_PORT_MAX' not described in enum 'wwan_port_type'