[Dev] Chromebook C201 wifi

[Denis 'GNUtoo' Carikli]

On Sat, 30 Mar 2019 17:21:54 -0400
Lee Strobel <leestrobel at disroot.org> wrote:

> Hi,
Hi,

> I saw that several posts have been made on this page regarding wifi
> for the Chromebook C201:
For the record, the WiFi related bugreport is here:
https://labs.parabola.nu/issues/2261

Could you try to see if a USB HUB that is powered by its own power
supply makes it usable. If you don't have one you may know people that
have one and borrow it just for doing a quick test.

> It seems fairly serious for the C201, because if
> there is no viable option for wifi, then it's going to significantly
> limit its usefulness for a 100% free distro.
We have similar issues with Replicant, and for now we also rely on
external WiFi dongles. The WiFi stability is also a concern, and not
all supported smartphones are equals in that regard.

One way to gather more information on the issue would be to research
how much mA the USB ports are able to provide.

A "Technoethical N150 Mini Wireless USB Adapter"[1] require 500mA, and
other ath9k_htc compatible USB wireless adapters I tested also require
500mA:
> # lsusb -d 0cf3:9271 -vvvv
> [...]
> MaxPower              500mA

So if that Chromebook is not able to provide the 500mA, then it would
not be surprising if you have some stability issues.

The WiFi dongle firmware is free software, so it may be possible to
modify it not to consume that much power, but as far as I know no one
started investigating if that is possible or not yet.

> I am just wondering if anyone knows whether the kernel developers are
> aware of this issue?
In Replicant, of the ways we use to find how much mA can be provided is
to look at the Linux source code, and/or at the datasheets/reference
manual of the chips involved providing power to the USB devices.
However sometimes the information is missing from the kernel drivers
and the hardware reference manuals can't be found on the Internet.

As the linux-libre-chromebook kernel is the same than linux-libre, but
it is packaged to be able to run on a chromebook, the information that
is in upstream Linux should also apply here.

The only differences between both linux-libre and linux-libre-chromebook
is that a vmlinux.kpart file is created from the kernel image and a
post_install script handles flashing that created file.

Reference:
----------
[1]https://tehnoetic.com/tehnoetic-wireless-adapter-gnu-linux-libre-tet-n150

Denis.
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