[OpenWrt-Devel] [RFC/RFT PATCH] ath9k: implement kthread entropy collection for AR5008 and AR9002 PHYs.

[Rui Salvaterra]

Hi, Felix,

On Fri, 31 Jan 2020 at 08:12, Felix Fietkau <nbd at nbd.name> wrote:
> For at least AR5008 and AR9002, but probably also for AR9003 I would
> like to keep the behavior of collecting entropy only once at driver
> initialization.

Well, you could have told me this before I started working on it, but
I guess you
don't read the developer section of the forum, even when you're mentioned. ;)
(What's the best communication channel for OpenWrt development? There are
far too many options, I think.)

FWIW, my Archer C6 v2 has been running OpenWrt 19.07 with my entropy
patch for days without any problems (1 x AR9003, though). I'll be testing soon
on a TL-WDR3600 (2 x AR9003) and a WNDR3700 v1 (2 x AR9002). Like
I wrote in the forum, I don't have (yet) AR5008 hardware to test.

> Last time I worked on this I noticed that on several chips, sampling
> entropy during normal operation caused stability issues that were hard
> to pin down but quite noticeable.

Maybe it's not a good idea to sample from a low power state? :) The old code
didn't call ath9k_ps_wakeup before collecting (and ath9k_ps_restore afterwards),
it's possible that the stability problems are related to the power
state at collection
time.

The current mainline code is from 2015, and it's nothing like the one in the
OpenWrt patch (from 2013). The entropy collection is not continuous at all,
it's done on a kthread which only wakes up when the available entropy drops
below a certain threshold. I only extended the mainline code to support the
previous PHYs.

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