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The signal-to-noise-ratio SNR is returned by the wcn36xx firmware for each
received frame. SNR represents all of the unwanted interference signal
after filtering out the fundamental frequency and harmonics of the
frequency.
Noise can come from various electromagnetic sources, from temperature
affecting the performance hardware components or quantization effects
converting from analog to digital domains.
The SNR value returned by the WiFi firmware then is a good source of
entropy.
Other WiFi drivers offer up the noise component of the FFT as an entropy
source for the random pool e.g.
commit 2aa56cca35 ("ath9k: Mix the received FFT bins to the random pool")
I attended Jason's talk on sources of randomness at Plumbers and it
occurred to me that SNR is a reasonable candidate to add.
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220915004117.1562703-2-bryan.odonoghue@linaro.org
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.