linux-kernel - Re: [PATCH] IB/mad: Use ID allocator routines to allocate agent number

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Date:   Tue, 29 May 2018 09:49:22 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Hans Westgaard Ry <hans.westgaard.ry@...cle.com>
Cc:     Doug Ledford <dledford@...hat.com>,
        Hakon Bugge <haakon.bugge@...cle.com>,
        Jack Morgenstein <jackm@....mellanox.co.il>,
        Daniel Jurgens <danielj@...lanox.com>,
        Parav Pandit <parav@...lanox.com>,
        Pravin Shedge <pravin.shedge4linux@...il.com>,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] IB/mad: Use ID allocator routines to allocate agent
 number

On Tue, May 29, 2018 at 09:38:08AM +0200, Hans Westgaard Ry wrote:
> The agent TID is a 64 bit value split in two dwords.  The least
> significant dword is the TID running counter. The most significant
> dword is the agent number. In the CX-3 shared port model, the mlx4
> driver uses the most significant byte of the agent number to store the
> slave number, making agent numbers greater and equal to 2^24 (3 bytes)
> unusable.

There is no reason for this to be an ida, just do something like

 mad_agent_priv->agent.hi_tid = atomic_inc_return(&ib_mad_client_id) & mad_agent_priv->ib_dev->tid_mask;

And have the driver set tid_mask to 3 bytes of 0xFF

And no sysctl.

Jason