netdev - Re: [PATCH net-next 03/12] net: atlantic: changes for multi-TC support

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Message-ID: <20200520140154.6b6328de@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 20 May 2020 14:01:54 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Igor Russkikh <irusskikh@...vell.com>
Cc:     <netdev@...r.kernel.org>, "David S . Miller" <davem@...emloft.net>,
        Mark Starovoytov <mstarovoitov@...vell.com>,
        Dmitry Bezrukov <dbezrukov@...vell.com>
Subject: Re: [PATCH net-next 03/12] net: atlantic: changes for multi-TC
 support

On Wed, 20 May 2020 16:47:25 +0300 Igor Russkikh wrote:
> From: Dmitry Bezrukov <dbezrukov@...vell.com>
> 
> This patch contains the following changes:
> * add cfg->is_ptp (used for PTP enable/disable switch, which
>   is described in more details below);
> * add cfg->tc_mode (A1 supports 2 HW modes only);
> * setup queue to TC mapping based on TC mode on A2;
> * remove hw_tx_tc_mode_get / hw_rx_tc_mode_get hw_ops.
> 
> In the first generation of our hardware (A1), a whole traffic class is
> consumed for PTP handling in FW (FW uses it to send the ptp data and to
> send back timestamps).
> Since this conflicts with QoS (user is unable to use the reserved TC2),
> we suggest using module param to give the user a choice: disabling PTP
> allows using all available TCs.

Is there really no way to get the config automatically chosen
when user sets up TCs or does SIOCSHWTSTAMP? It's fine to return
-EOPNOTSUPP when too many things are enabled, but user having to set
module parameters upfront is quite painful.