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From:   Brian Norris <briannorris@chromium.org>
Date:   Wed, 25 Mar 2020 11:14:48 -0700
Message-ID: <CA+ASDXNQxea+83+h87OQwDV-n_Sb8ENyEGx=BsJbMa3G9kkEVQ@mail.gmail.com>
Subject: Re: [PATCH] rtw88: add debugfs to fix tx rate
To:     Ben Greear <greearb@candelatech.com>
Cc:     Tony Chuang <yhchuang@realtek.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        Kalle Valo <kvalo@codeaurora.org>,
        "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>
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On Wed, Mar 25, 2020 at 8:52 AM Ben Greear <greearb@candelatech.com> wrote:
> On 03/24/2020 10:16 PM, Brian Norris wrote:
> > Sure, but if you mask out all but 1 bitrate...voila! A fixed rate!
>
> So, see this thread from a while back.  Has anyone even *tried* to use
> this API you are proposing?

Yes, in fact, I have! Which is why I noted:

> > Now, there are other problems, like the others that Ben mentioned: the
> > rest of the mac80211 framework doesn't like it too much if you really
> > disable all but 1 rate (arguably a mac80211 bug -- but not a nl80211
> > bug)

> http://lists.infradead.org/pipermail/ath10k/2017-October/010291.html

I hadn't seen that thread. So it sounds like maybe Johannes isn't
quite on the same page as Johannes ;)

If we're going to be particular about matching the AP's basic rates,
then this API is indeed probably not useful for the "single fixed rate
[for debugging/testing]" use case.

>      mac80211: Revert some of e8e4f5, fixes setting single rate in ath10k.

Commit e8e4f5 was an unfortunate consequence of the stuff I mentioned
earlier about how Chrome OS used to use SET_TX_BITRATE_MAX -- we
weren't nuanced about it at all, so we might configure a set of
bitrates that doesn't intersect at all with the AP's BasicRates. That
does make it hard for the driver/framework to decide what to do: do we
listen to the user, or to the AP? Incidentally, that's also one reason
why Chrome OS no longer uses the API; it was too big of a hammer for
what we want (initial-connection reliability), and required us to be
more delicate about {Supported,Basic}Rates than we really wanted to.

Brian