netdev - Re: [net-next] net: dsa: felix: disable always guard band bit for TAS config

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Date:   Mon, 19 Apr 2021 15:38:25 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Xiaoliang Yang <xiaoliang.yang_1@....com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Arvid.Brodin@...n.com,
        m-karicheri2@...com, vinicius.gomes@...el.com,
        michael.chan@...adcom.com, vishal@...lsio.com, saeedm@...lanox.com,
        jiri@...lanox.com, idosch@...lanox.com,
        alexandre.belloni@...tlin.com, UNGLinuxDriver@...rochip.com,
        ivan.khoronzhuk@...aro.org, andre.guedes@...ux.intel.com,
        yuehaibing@...wei.com, allan.nielsen@...rochip.com,
        joergen.andreasen@...rochip.com, colin.king@...onical.com,
        po.liu@....com, mingkai.hu@....com, claudiu.manoil@....com,
        vladimir.oltean@....com, leoyang.li@....com
Subject: Re: [net-next] net: dsa: felix: disable always guard band bit for
 TAS config

Hi Xiaoliang,

On Mon, Apr 19, 2021 at 06:25:30PM +0800, Xiaoliang Yang wrote:
> ALWAYS_GUARD_BAND_SCH_Q bit in TAS config register is descripted as
> this:
> 	0: Guard band is implemented for nonschedule queues to schedule
> 	   queues transition.
> 	1: Guard band is implemented for any queue to schedule queue
> 	   transition.
>
> The driver set guard band be implemented for any queue to schedule queue
> transition before, which will make each GCL time slot reserve a guard
> band time that can pass the max SDU frame. Because guard band time could
> not be set in tc-taprio now, it will use about 12000ns to pass 1500B max
> SDU. This limits each GCL time interval to be more than 12000ns.
>
> This patch change the guard band to be only implemented for nonschedule
> queues to schedule queues transition, so that there is no need to reserve
> guard band on each GCL. Users can manually add guard band time for each
> schedule queues in their configuration if they want.
>
> Signed-off-by: Xiaoliang Yang <xiaoliang.yang_1@....com>
> ---

What is a scheduled queue? When time-aware scheduling is enabled on the
port, why are some queues scheduled and some not?