netdev - Re: [PATCH net-next 10/13] tsnep: deny tc-taprio changes to per-tc max SDU

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Date:   Thu, 15 Sep 2022 21:01:19 +0200
From:   Gerhard Engleder <gerhard@...leder-embedded.com>
To:     Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        Rui Sousa <rui.sousa@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        UNGLinuxDriver@...rochip.com, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Michael Walle <michael@...le.cc>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        Maxim Kochetkov <fido_max@...ox.ru>,
        Colin Foster <colin.foster@...advantage.com>,
        Richie Pearn <richard.pearn@....com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Vladimir Oltean <olteanv@...il.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Grygorii Strashko <grygorii.strashko@...com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 10/13] tsnep: deny tc-taprio changes to per-tc
 max SDU

> Since the driver does not act upon the max_sdu argument, deny any other
> values except the default all-zeroes, which means that all traffic
> classes should use the same MTU as the port itself.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---
>   drivers/net/ethernet/engleder/tsnep_tc.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/engleder/tsnep_tc.c b/drivers/net/ethernet/engleder/tsnep_tc.c
> index c4c6e1357317..82df837ffc54 100644
> --- a/drivers/net/ethernet/engleder/tsnep_tc.c
> +++ b/drivers/net/ethernet/engleder/tsnep_tc.c
> @@ -320,11 +320,15 @@ static int tsnep_taprio(struct tsnep_adapter *adapter,
>   {
>   	struct tsnep_gcl *gcl;
>   	struct tsnep_gcl *curr;
> -	int retval;
> +	int retval, tc;
>   
>   	if (!adapter->gate_control)
>   		return -EOPNOTSUPP;
>   
> +	for (tc = 0; tc < TC_MAX_QUEUE; tc++)
> +		if (qopt->max_sdu[tc])
> +			return -EOPNOTSUPP;

Does it make any difference if the MAC already guarantees that too
long frames, which would violate the next taprio interval, will not
be transmitted? MACs are able to do that, switches not.

The user could be informed, that the MAC is considering the length of 
the frames by accepting any max_sdu value lower than the MTU of the netdev.