Message-ID: <20150825192827.GA16488@ketchup.mtl.sfl>
Date:	Tue, 25 Aug 2015 15:28:28 -0400
From:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
To:	Randy Dunlap <rdunlap@...radead.org>
Cc:	Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org,
	davem@...emloft.net, andrew@...n.ch, sfeldma@...il.com,
	linux@...ck-us.net,
	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
Subject: Re: [PATCH net-next v2 2/2] Documentation: networking: dsa: Add
 Broadcom SF2 document

Hi Florian,

If a respin is necessary for this 2/2 too, consider two nitpicks below.

On 15-08-25 11:47:18, Randy Dunlap wrote:
> On 08/25/15 10:40, Florian Fainelli wrote:
> > Add a document describing the Broadcom Starfigther 2 switch hardware,
> > its specifics, and how the driver is implemented and its specifics.

Redundant "specifics" word.

> > 
> > Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> > ---
> >  Documentation/networking/dsa/bcm_sf2.txt | 113 +++++++++++++++++++++++++++++++
> >  1 file changed, 113 insertions(+)
> >  create mode 100644 Documentation/networking/dsa/bcm_sf2.txt
> > 
> > diff --git a/Documentation/networking/dsa/bcm_sf2.txt b/Documentation/networking/dsa/bcm_sf2.txt
> > new file mode 100644
> > index 000000000000..7b1502bb707d
> > --- /dev/null
> > +++ b/Documentation/networking/dsa/bcm_sf2.txt
> > @@ -0,0 +1,113 @@
> > +Broadcom Starfighter 2 Ethernet switch driver
> > +=============================================
> > +
> > +Broadcom's Starfighter 2 Ethernet switch hardware block is commonly found and
> > +deployed in the following products:
> > +
> > +- xDSL gateways such as BCM63138
> > +- streaming/multimedia Set Top Box such as BCM7445
> > +- Cable Modem/residential gatewasy such as BCM7145/BCM3390

                               gateway

> > +
> > +The switch is typically deployed in a configuration involving between 5 to 13
> > +ports, offering a range of built-in and customizable interfaces:
> > +
> > +- single integrated Gigabit PHY
> > +- quad integrated Gigabit PHY
> > +- quad external Gigabit PHY w/ MDIO multiplexer
> > +- integrated MoCA PHY
> > +- several external MII/RevMII/GMII/RGMII interfaces
> > +
> > +The switch also supports specific congestion control features which allow MoCA
> 
> what is MoCA?  Maybe answer in "MoCA interfaces" section.
> 
> > +fail-over not to loose packets during a MoCA role re-election, as well as out of
> 
>                     lose
> 
> > +band back-pressure to the host CPU network interface when downstream interfaces
> > +are connected at a lower speed.
> > +
> > +The switch hardware block is typically interfaces using MMIO accesses and
> 
>                                           interfaced
> or drop the "is"
> 
> > +contains a bunch of sub-blocks/registers:
> > +
> > +SWITCH_CORE: common switch registers
> > +SWITCH_REG: external interfaces switch register
> > +SWITCH_MDIO: external MDIO bus controller (there is another one in SWITCH_CORE,
> > +which is used for indirect PHY accesses)
> > +SWITCH_INTRL2_0/1: Level-2 interrupt controllers
> > +SWITCH_ACB: Admission control block
> > +SWITCH_FCB: Fail-over control block
> > +
> > +Implementation details
> > +======================
> > +
> > +The driver is located in drivers/net/dsa/bcm_sf2.c and is implemented as a DSA
> > +driver, see Documentation/networking/dsa/dsa.txt for details on the subsytem and
> 
> s/,/;/
> 
> > +what it provides.
> > +
> > +The SF2 switch is configured to enable a Broadcom specific 4-bytes switch tag
> > +which gets inserted by the switch for every packet forwarded to the CPU
> > +interface, conversely, the CPU network interface should insert a similar tag for
> > +packets entering the CPU port. The tag format is described in
> > +net/dsa/tag_brcm.c.
> > +
> > +Overall, the SF2 driver is a fairly regular DSA driver, there are a few
> 
>                          s/,/;/ here.....................^
> 
> > +specifics covered below.
> > +
> > +Device Tree probing
> > +-------------------
> > +
> > +The DSA platform device driver is probed using a specific compatible string
> > +provided in net/dsa/dsa.c. The reason for that is because the DSA subsystem gets
> > +registered as a platform device driver currently. DSA will provide the needed
> > +device_node pointers which are then accessible by the switch driver setup
> > +function to setup resources such as register ranges and interrupts. This
> > +currently works very well because none of the of_* functions utilized by the
> > +driver require a struct device to be bound to a struct device_node, but things
> > +may change in the future.
> > +
> > +MDIO indirect accesses
> > +----------------------
> > +
> > +Due to a limitation in how Broadcom switches have been designed, external
> > +Broadcom switches connected to a SF2 require the use of the DSA slave MDIO bus
> > +in order to properly configure them. By default, the SF2 pseudo-PHY address, and
> > +an external switch pseudo-PHY address will both be snooping for incoming MDIO
> > +transactions, since they are at the same address (30), resulting in some kind of
> > +"double" programming. Using DSA, and setting ds->phys_mii_mask accordingly, we
> > +selectively divert reads and writes towards external Broadcom switches
> > +pseudo-PHY addresses. Newer revisions of the SF2 hardware have introduced a
> > +configurable pseudo-PHY address which circumvents the initial design limitation.
> > +
> > +MoCA interfaces
> > +---------------
> > +
> > +MoCA interfaces are fairly specific and require the use of a firmware blob which
> > +gets loaded onto the MoCA processor(s) for packet processing. The switch
> > +hardware contains logic which will assert/de-assert link states accordingly for
> > +the MoCA interface whenever the MoCA coaxial cable gets disconnected or the
> > +firmware gets reloaded. The SF2 driver relies on such events to properly set its
> > +MoCA interface carrier state and properly report this to the networking stack.
> > +
> > +The MoCA interfaces are supported using the PHY library's fixed PHY/emulated PHY
> > +device and the switch driver registers a fixed_link_update callback for such
> > +PHYs which reflects the link state obtained from the interrupt handler.

Best,
-v
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