linux-kernel - RE: [PATCH net-next 3/5] net: mvpp2: use a data size of 10kB for Tx FIFO on port 0

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Date:   Sun, 4 Mar 2018 06:29:59 +0000
From:   Stefan Chulski <stefanc@...vell.com>
To:     Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Antoine Tenart <antoine.tenart@...tlin.com>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        Yan Markman <ymarkman@...vell.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "maxime.chevallier@...tlin.com" <maxime.chevallier@...tlin.com>,
        "gregory.clement@...tlin.com" <gregory.clement@...tlin.com>,
        "miquel.raynal@...tlin.com" <miquel.raynal@...tlin.com>,
        Nadav Haklai <nadavh@...vell.com>,
        "mw@...ihalf.com" <mw@...ihalf.com>
Subject: RE: [PATCH net-next 3/5] net: mvpp2: use a data size of 10kB for Tx
 FIFO on port 0


> On Fri,  2 Mar 2018 16:40:42 +0100, Antoine Tenart wrote:
> 
> > -/* Initialize Tx FIFO's */
> > +/* Initialize Tx FIFO's
> > + * The CP110's total tx-fifo size is 19kB.
> > + * Use large-size 10kB for fast port but 3kB for others.
> > + */
> 
> Is there a reason to hardcode 10KB for port 0, and 3KB for the other ports ?
> Would there be use cases where the user may want different configurations
> ?
> 

Design requirement are 10KB TX FIFO for the 10Gb/sec and 2.5KB for the 2.5Gb/sec.
Since only port 0 support 10Gb/sec and ports 1&2 support up to 2.5Gb/sec.
I don't see any reason to change this configurations.
Also TX FIFO size could be set only during probe.

> It's just that it feels very "hardcoded" to enforce specifically those numbers.
> 
> Also, does it make sense to mention the CP110 here ? Is this 19 KB limitation
> a limit of the PPv2.2 IP, or of the CP110 ?

PPv2.2 IP is part of 110 communication processor.
Next communication processor will has different Packet processor or next generation of PPv2.x
Limit is PPv2.2 TX FIFO.

Stefan.