linux-kernel - Re: [PATCH net-next v4] wwan dev: Add port for NMEA channel for WWAN devices

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Message-ID: <CAMZdPi91hR10xe=UzccqtwvtvS9_Wf9NEw6i5-x=e4UdfKMcug@mail.gmail.com>
Date: Mon, 6 Jan 2025 20:44:35 +0100
From: Loic Poulain <loic.poulain@...aro.org>
To: Muhammad Nuzaihan <zaihan@...ealasia.net>, Slark Xiao <slark_xiao@....com>
Cc: Sergey Ryazanov <ryazanov.s.a@...il.com>, Johannes Berg <johannes@...solutions.net>, 
	Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v4] wwan dev: Add port for NMEA channel for WWAN devices

Hi Muhammad,

+ Slark

On Sun, 5 Jan 2025 at 13:53, Muhammad Nuzaihan <zaihan@...ealasia.net> wrote:
>
> Based on the code: drivers/bus/mhi/host/pci_generic.c
> which already has NMEA channel (mhi_quectel_em1xx_channels)
> support in recent kernels but it is never exposed
> as a port.
>
> This commit exposes that NMEA channel to a port
> to allow tty/gpsd programs to read through
> the /dev/wwan0nmea0 port.
>
> Tested this change on a new kernel and module
> built and now NMEA (mhi0_NMEA) statements are
> available (attached) through /dev/wwan0nmea0 port on bootup.
>
> Signed-off-by: Muhammad Nuzaihan Bin Kamal Luddin <zaihan@...ealasia.net>

This works for sure but I'm not entirely convinced NMEA should be
exposed as a modem control port. In your previous patch version Sergey
pointed to a discussion we had regarding exposing that port as WWAN
child device through the regular GNSS subsystem, which would require
some generic bridge in the WWAN subsystem.

Slark, did you have an opportunity to look at the GNSS solution?

Regards,
Loic