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Date:   Wed, 15 May 2019 15:48:29 +0200
From:   Stanislaw Gruszka <sgruszka@redhat.com>
To:     Lorenzo Bianconi <lorenzo@kernel.org>
Cc:     Kalle Valo <kvalo@codeaurora.org>, nbd@nbd.name,
        lorenzo.bianconi@redhat.com, linux-wireless@vger.kernel.org
Subject: Re: [PATCH] mt76: mt7603: add debugfs knob to enable/disable edcca
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On Wed, May 15, 2019 at 02:07:42PM +0200, Lorenzo Bianconi wrote:
> > On Wed, May 15, 2019 at 01:13:49PM +0200, Lorenzo Bianconi wrote:
> > > > On Wed, May 15, 2019 at 12:03:44PM +0200, Lorenzo Bianconi wrote:
> > > > > > On Wed, May 15, 2019 at 11:43:55AM +0200, Lorenzo Bianconi wrote:
> > > > > > > > On Mon, May 13, 2019 at 11:48:37AM +0200, Stanislaw Gruszka wrote:
> > > > > > > > > On Mon, May 13, 2019 at 10:41:28AM +0200, Lorenzo Bianconi wrote:
> > > > > > > > > > > Lorenzo Bianconi <lorenzo@kernel.org> writes:
> > > > > > > > > > > 
> > > > > > > > > > > > Introduce a knob in mt7603 debugfs in order to enable/disable
> > > > > > > > > > > > edcca processing
> > > > > > > > > > > >
> > > > > > > > > > > > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > > > > > > > > > > 
> > > > > > > > > > > It's good to explain what edcca does and how the file is used supposed
> > > > > > > > > > > to be used. In other words, have a small introduction for the user.
> > > > > > > > > > 
> > > > > > > > > > Hi Kalle,
> > > > > > > > > > 
> > > > > > > > > > edcca is used for adjusting energy detect based on CCA thresholds.
> > > > > > > > > > The code was already there so I just reported the acronym.
> > > > > > > > > 
> > > > > > > > > What for it is needed ?
> > > > > > > > 
> > > > > > > > Care to comment why EDCCA is needed at all ?
> > > > > > > > 
> > > > > > > > Taking that debugfs file that enable it is read-only, it looks like
> > > > > > > > feature that nobody needs nor tests.
> > > > > > > 
> > > > > > > already fixed in v2
> > > > > > > https://patchwork.kernel.org/patch/10940645/
> > > > > > 
> > > > > > I'm aware of this patch and other one for mt76x02. But so far in the
> > > > > > sources EDCCA is disabled for mt76x02 without possibility to enable it
> > > > > > (and this permission file issue was pointed by Kalle during review, not
> > > > > > by someone who want to test EDCCA). So again, what for EDCCA is needed ?
> > > > > 
> > > > > As I have already written in a previous email, ED/CCA is used to control tx power
> > > > > according to the CCA MIB counters (e.g do not transmit if the channel busy time
> > > > > is higher than 90% for given amount of time in a row). I guess it is required
> > > > > by ETSI regulatory.
> > > > But what is user case for that, i.e. who need this (it wasn't implemented in
> > > > mt76x2 since you added it on Dec 2018). What will happen if it will be removed?
> > > > 
> > > > > Regarding file permission for mt76x02 debugfs edcca node is a typo.
> > > > Typo or not, effectively disable the feature and show nobody is
> > > > testing it.
> > > > 
> > > > The reason I'm asking is that seems EDCCA is the main reason to
> > > > implement watchod for mt76x2, it wasn't necessary to have a watchdog
> > > > as seems devices did not hung before EDCCA was added.
> > > 
> > > IIRC I added the first watchdog implementation to fix tx hangs that occur
> > > under heavy load even using FCC regulatory (so when EDCCA processing is
> > > disabled)
> > 
> > There was changes in various registers programming introduced by EDCCA
> > support, even with EDCCA disabled. It's rally not convenient that
> > watchdog and EDCCA are not related, since you added tx hung watchdog
> > 2 weeks after adding EDCCA.
> > 
> > You can look at this report:
> > https://github.com/openwrt/mt76/issues/246
> > Before mt76x2e worked without hungs & watchodg. Now, even with EDCCA
> > disabled watchdog and HW restarts are required to fix hungs on runtime.
> 
> Tx hangs occur in very particular conditions (e.g 200Mbps bidirectional
> traffic) and moreover they do not always occur so I am not convinced they
> are always EDCCA related and so I am not confident to remove the watchdog

I'm not opting for watchdog removal, but for full EDCCA removal.
Apparently nobody cares, if it can be enabled or not.

Stanislaw