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Subject: Re: [PATCH] rtw88: add debugfs to fix tx rate
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Brian Norris <briannorris@chromium.org>,
        Ben Greear <greearb@candelatech.com>
Cc:     Tony Chuang <yhchuang@realtek.com>,
        Kalle Valo <kvalo@codeaurora.org>,
        "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>
Date:   Mon, 25 May 2020 11:07:00 +0200
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On Wed, 2020-03-25 at 11:14 -0700, Brian Norris wrote:
> 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 ;)

Hah. Happens all the time, not sure what that other Johannes is thinking
;-)

More seriously though, I'm a bit lost now (and a big part of that is
probably because I'm replying to a 2 months old thread, sorry).

> 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.

Right.

But I'm not sure why Ben needs to just do a pr_err()? Shouldn't that
just not happen?

Hmm.

johannes