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Date:   Fri, 20 Nov 2020 03:25:40 +0100
From:   Andrew Lunn <andrew@lunn.ch>
To:     DENG Qingfang <dqfext@gmail.com>
Cc:     netdev@vger.kernel.org, linux-mediatek@lists.infradead.org,
        Sean Wang <sean.wang@mediatek.com>,
        Landen Chao <Landen.Chao@mediatek.com>,
        Vivien Didelot <vivien.didelot@gmail.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Vladimir Oltean <olteanv@gmail.com>,
        "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Russell King <linux@armlinux.org.uk>,
        =?iso-8859-1?Q?Ren=E9?= van Dorst <opensource@vdorst.com>,
        Frank Wunderlich <frank-w@public-files.de>,
        Greg Ungerer <gerg@kernel.org>,
        Alex Dewar <alex.dewar90@gmail.com>,
        Chuanhong Guo <gch981213@gmail.com>
Subject: Re: [RFC PATCH net-next] net: dsa: mt7530: support setting ageing
 time
Message-ID: <20201120022540.GD1804098@lunn.ch>
References: <20201119064020.19522-1-dqfext@gmail.com>
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On Thu, Nov 19, 2020 at 02:40:20PM +0800, DENG Qingfang wrote:
> MT7530 has a global address age control register, so use it to set
> ageing time.
> 
> The applied timer is (AGE_CNT + 1) * (AGE_UNIT + 1) seconds
> 
> Signed-off-by: DENG Qingfang <dqfext@gmail.com>
> ---
>  drivers/net/dsa/mt7530.c | 41 ++++++++++++++++++++++++++++++++++++++++
>  drivers/net/dsa/mt7530.h | 13 +++++++++++++
>  2 files changed, 54 insertions(+)
> 
> RFC:
> 1. What is the expected behaviour if the timer is too big or too small?
>    - return -ERANGE or -EINVAL;

ERANGE is good. 

>      or
>    - if it is too big, apply the maximum value; if it is too small,
>      disable learning;
> 
> 2. Is there a better algorithm to find the closest pair?

The bridge code will default to 300 seconds. And after a topology
change, it sets it to 2 * the forwarding delay, which defaults to 15
seconds. So maybe you can look for these two values, and use
pre-computed values?

You still need to handle other values, the user can configure these.

	     Andrew