XPost: linux.debian.kernel

Source: linux
Severity: minor

Hi,
I've been taking an interest in GPS/GNSS lately and improving the user experience in particular, so I'm glad to see that the kernel's GNSS subsystem is enabled. However, it looks like a couple modules adding support for additional hardware is not yet
enabled and in the absence of a reason otherwise I'd like to see them built as well:
$ unxz < /usr/src/linux-config-6.14/config.arm64_none_arm64.xz | grep -F GNSS CONFIG_GNSS=m
CONFIG_GNSS_SERIAL=m
# CONFIG_GNSS_MTK_SERIAL is not set
CONFIG_GNSS_SIRF_SERIAL=m
CONFIG_GNSS_UBX_SERIAL=m
# CONFIG_GNSS_USB is not set

This configuration is nothing new; the Trixie/amd64 kernel is the same and it's probably been this way for a while.

Here "MTK_SERIAL" refers to MediaTek's GNSS modules which are pretty popular with DIY-ers and are used, for example, in Adafruit's Ultimate GPS modules. Enabling that module and presumably CONFIG_GNSS_USB as well will help with device enumeration which
is currently a hot mess. Because these are serial devices probing for hardware isn't very practical, and in particular there is no USB device class for these types of devices, so they only clearly identify themselves as serial converters.
Nevertheless, this subsystem allows for device identification and management to be better handled by udev, Devicetree, and the like. This will certainly help embedded systems and automotive electronics right away; my interest was ignited by wanting a
navigation system for cycling. Dealing with baud rate changes and such tweaks is very tricky at the moment; MediaTek's modules support increasing the baud rate of the GNSS receiver, and when 'stty' or termios(3) is used to adjust the speed of your host's
serial interface in lockstep, this works great for getting more frequent data. However terminal device attributes can change underneath you after the last file descriptor to the device is closed, but on the MediaTek receiver's side of the link it'll
still be happily using the custom speed for transmission. This creates a nasty surprise when the device is opened again; opening the device is often done only when necessary to save power and give the GNSS receiver a break.

Admittedly I haven't gotten to try out the GNSS subsystem yet or make these changes, but Debian is very well-suited for those navigation devices that could benefit the most, so enabling these modules to be built on all architectures would be nice.

Thanks

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