linux-kernel - Re: [PATCH net-next v3 1/2] net: mscc: ocelot: Add support for tcam

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Date:   Sat, 26 Sep 2020 13:20:02 +0200
From:   Horatiu Vultur <horatiu.vultur@...rochip.com>
To:     Vladimir Oltean <olteanv@...il.com>
CC:     Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        "Ralf Baechle" <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        "James Hogan" <jhogan@...nel.org>, <linux-mips@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        "Allan W. Nielsen" <allan.nielsen@...rochip.com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        <hongbo.wang@....com>
Subject: Re: [PATCH net-next v3 1/2] net: mscc: ocelot: Add support for tcam

The 09/25/2020 02:39, Vladimir Oltean wrote:
> 
Hi Vladimir,

> Hi Horatiu,
> 
> On Thu, Apr 23, 2020 at 10:29:48AM +0200, Horatiu Vultur wrote:
> > > > +static const struct vcap_props vcap_is2 = {
> > > > +       .name = "IS2",
> > > > +       .tg_width = 2,
> > > > +       .sw_count = 4,
> > > > +       .entry_count = VCAP_IS2_CNT,
> > > > +       .entry_words = BITS_TO_32BIT(VCAP_IS2_ENTRY_WIDTH),
> > > > +       .entry_width = VCAP_IS2_ENTRY_WIDTH,
> > > > +       .action_count = (VCAP_IS2_CNT + VCAP_PORT_CNT + 2),
> > > > +       .action_words = BITS_TO_32BIT(VCAP_IS2_ACTION_WIDTH),
> > > > +       .action_width = (VCAP_IS2_ACTION_WIDTH),
> > > > +       .action_type_width = 1,
> > > > +       .action_table = {
> > > > +               {
> > > > +                       .width = (IS2_AO_ACL_ID + IS2_AL_ACL_ID),
> > > > +                       .count = 2
> > > > +               },
> > > > +               {
> > > > +                       .width = 6,
> > > > +                       .count = 4
> > > > +               },
> > > > +       },
> > > > +       .counter_words = BITS_TO_32BIT(4 * ENTRY_WIDTH),
> > > > +       .counter_width = ENTRY_WIDTH,
> > > > +};
> 
> Coming again to this patch, I'm having a very hard time understanding
> how VCAP_IS2_ENTRY_WIDTH is derived and what it represents, especially
> since the VCAP_CONST_ENTRY_WIDTH register reads something different.
> Could you please explain?

To be honest, I don't remember precisely. I will need to setup a board
and see exactly. But from what I remember:
- according to this[1] in chapter 3.8.6, table 71. It says that the full
  entry of IS2 is 384. And this 384 represent a full entry. In this row,
  can be also sub entries like: half entry and quater entries. And each
  entry has 2 bits that describes the entry type. So if you have 2 bits
  for each possible entry then you have 8 bits describing each type. One
  observation is even if you have a full entry each pair of 2 bits
  describing the type needs to be set that is a full entry. Maybe if you
  have a look at Figure 30, it would be a little bit more clear. Even
  there is a register called VCAP_TG_DAT that information is storred
  internally in the VCAP_ENTRY_DAT.
- so having those in mind, then VCAP_IS2_ENTRY_WIDTH is the full entry
  length - 8 bits. 384 - 8 = 376.
- then if I remember correctly then VCAP_CONST_ENTRY_WIDTH should be
  384? or 12 if it is counting the words.

Does it make sense or am I completly off?

> 
> Thanks,
> -Vladimir

[1] http://ww1.microchip.com/downloads/en/DeviceDoc/VMDS-10491.pdf

-- 
/Horatiu