netdev - Re: [PATCHv2 net-next 09/11] net: mvpp2: simplify MVPP2_PRS_RI

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Message-ID: <20170106130727.GB14217@n2100.armlinux.org.uk>
Date:   Fri, 6 Jan 2017 13:07:27 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>,
        Yehuda Yitschak <yehuday@...vell.com>,
        Jason Cooper <jason@...edaemon.net>,
        Hanna Hawa <hannah@...vell.com>,
        Nadav Haklai <nadavh@...vell.com>,
        Gregory Clement <gregory.clement@...e-electrons.com>,
        Stefan Chulski <stefanc@...vell.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        linux-arm-kernel@...ts.infradead.org,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCHv2 net-next 09/11] net: mvpp2: simplify MVPP2_PRS_RI_*
 definitions

On Wed, Dec 28, 2016 at 05:46:05PM +0100, Thomas Petazzoni wrote:
> Some of the MVPP2_PRS_RI_* definitions use the ~(value) syntax, which
> doesn't compile nicely on 64-bit. Moreover, those definitions are in
> fact unneeded, since they are always used in combination with a bit
> mask that ensures only the appropriate bits are modified.
> 
> Therefore, such definitions should just be set to 0x0. For example:
> 
>  #define MVPP2_PRS_RI_L2_CAST_MASK              0x600
>  #define MVPP2_PRS_RI_L2_UCAST                  ~(BIT(9) | BIT(10))
>  #define MVPP2_PRS_RI_L2_MCAST                  BIT(9)
>  #define MVPP2_PRS_RI_L2_BCAST                  BIT(10)
> 
> becomes
> 
>  #define MVPP2_PRS_RI_L2_CAST_MASK              0x600
>  #define MVPP2_PRS_RI_L2_UCAST                  0x0
>  #define MVPP2_PRS_RI_L2_MCAST                  BIT(9)
>  #define MVPP2_PRS_RI_L2_BCAST                  BIT(10)

So this is a two-bit field in a register with three defined states - I'm
not sure that using BIT() here is really a good idea.  BIT() is fine for
single-bit controls, but I think it adds an additional level of confusion
for multi-bit controls.

Also, the combination of the mask being defined as hex and the controls
using BIT() is particularly not nice.  I think either use one style or
the other, don't mix them.  So either:

  #define MVPP2_PRS_RI_L2_CAST_MASK              0x600
  #define MVPP2_PRS_RI_L2_UCAST                  0x000
  #define MVPP2_PRS_RI_L2_MCAST                  0x200
  #define MVPP2_PRS_RI_L2_BCAST                  0x400

or:

  #define MVPP2_PRS_RI_L2_CAST_MASK              (BIT(10) | BIT(9))
  #define MVPP2_PRS_RI_L2_UCAST                  0
  #define MVPP2_PRS_RI_L2_MCAST                  BIT(9)
  #define MVPP2_PRS_RI_L2_BCAST                  BIT(10)

It then becomes obvious that the mask and the settings are changing the
same bits.

-- 
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