Re: ath10k: antenna bitmask support?

From: Sebastian Gottschall <s.gottschall@dd-wrt.com>
To: Brian Norris <briannorris@chromium.org>
Cc: greearb@candelatech.com, ath10k@lists.infradead.org
Subject: Re: ath10k: antenna bitmask support?
Date: Tue, 7 Aug 2018 09:22:31 +0200	[thread overview]
Message-ID: <cd1f2332-44fa-917f-2a72-3bc52757e109@dd-wrt.com> (raw)
In-Reply-To: <CA+ASDXMwpaS93C_7pHzJGoaZZm7b_BSQkpGgngUuT7ney70vEw@mail.gmail.com>

Hello Brian

Am 07.08.2018 um 07:01 schrieb Brian Norris:
> Thanks for your response. The thing is, masks like 0x2 and 0x4 *do*
> appear to work for IPQ8064, as I noted above. Let me elaborate.
>
> I tested with a conductively-wired setup, where antennas are wired
> directly from an AP to a client (with reasonable attenuation), only 2
> of the 3 AP antennas are connected, and the client supports reporting
> signal strength on a per-antenna basis. If I set the AP's mask to 0x1,
> I see strong signal only on the client's antenna 1; if set to 0x2, I
> see strong signal only on the client's antenna 2; and if I set it to
> 0x4, I see only a very weak signal (presumably over the air, even
> without any antenna).
>
> In other words, I think this clearly works for some chipsets. I just
> wonder if anybody knows anything about why it does or doesn't work on
> a give chipset.
i dont think so. even if you see a signal on it i'm pretty sure that the 
rate control algorithm within the firmware
will simply fail and gets out of control due the way the rate control 
algorithm works and handles the chain controls.
depending on the rate the rate control algorithm will select chains to 
transmit. so i assume if you set it to 0x2, all rates
which are supported by 1x1 only, will not work anymore. so 1x1 clients 
simply wont work anymore.
and then there are several other cases like vht160, which always uses 
chain 1 and 2 even if 4x4 is selected. so if you configure
such a setup i expect nothing more than a crash in the firmware on 9984 
chipsets for instance
but of course these are assumptions from the firmware code i know and no 
proof.
Sebastian

>
> I also acknowledge that while the firmware may work properly, ath10k
> may not always account for this properly (hence, proposals like the
> diff in the previous email). I see several occasions where ath10k does
> a simple integer greater/less-than comparison between 1 and
> cfg_{tx,rx}_chainmask, which seems wrong. But my question is more
> geared toward firmware and hardware support; fixing drivers is
> relatively easy ;)
>
> Regards,
> Brian
>

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