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Date: Fri, 15 May 2026 17:37:26 +0100
From: Simon Horman <horms@kernel.org>
To: David Yang <mmyangfl@gmail.com>
Cc: netdev@vger.kernel.org, andrew@lunn.ch, olteanv@gmail.com,
	davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
	pabeni@redhat.com, jhs@mojatatu.com, jiri@resnulli.us,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next v3 2/2] net: dsa: yt921x: Add port TBF support
Message-ID: <20260515163726.GB227382@horms.kernel.org>
References: <20260508065757.2566258-3-mmyangfl@gmail.com>
 <20260512091026.279150-2-horms@kernel.org>
 <CAAXyoMOiokO-yh7AVs6qXDZzfM3PVYUDRKHY7FdXivjpcH=5mg@mail.gmail.com>
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On Fri, May 15, 2026 at 01:55:58AM +0800, David Yang wrote:
> On Tue, May 12, 2026 at 5:12 PM Simon Horman <horms@kernel.org> wrote:
> > Is it intended to return 0 here without populating the hardware statistics?
> >
> > When the driver handles this command by returning 0 without modifying
> > qopt->stats, it incorrectly signals to the TC core that hardware statistics
> > were successfully fetched. As a result, the subsystem will report
> > unmodified (typically zeroed) statistics, which hides any packets shaped
> > or dropped by the hardware.
> 
> https://lore.kernel.org/all/20260507012311.2187979-1-kuba@kernel.org/

Sorry for not noticing that earlier.

> Would a stub TC_TBF_STATS case that returns 0 (leaving bstats/qstats
> untouched) preserve the flag here?  mlxsw does this in its
> spectrum_qdisc.c.

Maybe adding a comment is sufficient.

> (also trying to address that in
> https://lore.kernel.org/r/20260509122238.2792915-1-mmyangfl@gmail.com)

Nice, thanks.

> 
> > Should this read the hardware statistic registers (like the newly defined
> > YT921X_PORTn_SHAPE_STAT) to update qopt->stats, or alternatively return
> > -EOPNOTSUPP to indicate a lack of support?
> 
> YT921X_PORTn_SHAPE_STAT gives the token bucket statistic, not flow meter.
> 
> (Not a real problem, but trying to suppress further AI gossip)

Ack.