linux-kernel - RE: [PATCH RFC] Update documentation for KSZ DSA drivers so that new drivers can be added

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Message-ID: <93AF473E2DA327428DE3D46B72B1E9FD41121E68@CHN-SV-EXMX02.mchp-main.com>
Date:   Fri, 8 Sep 2017 18:40:10 +0000
From:   <Tristram.Ha@...rochip.com>
To:     <andrew@...n.ch>, <muvarov@...il.com>
CC:     <pavel@....cz>, <nathan.leigh.conrad@...il.com>,
        <vivien.didelot@...oirfairelinux.com>, <f.fainelli@...il.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <Woojung.Huh@...rochip.com>
Subject: RE: [PATCH RFC] Update documentation for KSZ DSA drivers so that
 new drivers can be added

> -----Original Message-----
> From: Andrew Lunn [mailto:andrew@...n.ch]
> Sent: Friday, September 08, 2017 7:12 AM
> To: Maxim Uvarov
> Cc: Tristram Ha - C24268; Pavel Machek; Nathan Conrad; Vivien Didelot; Florian
> Fainelli; netdev; linux-kernel@...r.kernel.org; Woojung Huh - C21699
> Subject: Re: [PATCH RFC] Update documentation for KSZ DSA drivers so that new
> drivers can be added
> 
> On Fri, Sep 08, 2017 at 04:32:35PM +0300, Maxim Uvarov wrote:
> > 2017-09-08 0:54 GMT+03:00 Andrew Lunn <andrew@...n.ch>:
> > >> -- compatible: For external switch chips, compatible string must be exactly
> one
> > >> -  of: "microchip,ksz9477"
> > >> +- compatible: Should be "microchip,ksz9477" for KSZ9477 chip,
> > >> +           "microchip,ksz8795" for KSZ8795 chip,
> > >> +           "microchip,ksz8794" for KSZ8794 chip,
> > >> +           "microchip,ksz8765" for KSZ8765 chip,
> > >> +           "microchip,ksz8895" for KSZ8895 chip,
> > >> +           "microchip,ksz8864" for KSZ8864 chip,
> > >> +           "microchip,ksz8873" for KSZ8873 chip,
> > >> +           "microchip,ksz8863" for KSZ8863 chip,
> > >> +           "microchip,ksz8463" for KSZ8463 chip
> > >
> >
> > all that chips have the same spi access to get chip id on probe(). I
> > prefer common microship,ksz-spi rather than somebody will always
> > maintain that list.
> 
> The Marvell DSA driver is similar. The compatibility string tells you
> enough to go find the switch ID in the switch itself.
> 
> I suppose this comes down to, is there going to be one SPI driver for
> all the devices, or lots of drivers? In general, DSA has one driver
> for lots of devices. The mv88e6xxx supports around 25 devices. The b53
> has around 17, etc.
> 
> So i would suggest one driver supporting all the different devices.
> 

There will be 5 drivers to support these devices:

ksz9477.c - KSZ9893/KSZ9897/KSZ9567/KSZ9566/KSZ9477
ksz8795.c - KSZ8795/KSZ8795/KSZ8765
ksz8895.c - KSZ8895/KSZ8864
ksz8863.c - KSZ8863/KSZ8873
ksz8463.c - KSZ8463

These chips have different SPI access mechanisms, MIB counter reading,
and register set.  These can be combined into one single driver using
function pointers, at least for ksz8795/ksz8895/ksz8863/ksz8463.  My
only concern is the memory footprint.  The customer may not want a
big driver to cover all the switches while only one is used.

Out of topic I have a question to ask the community regarding the DSA
port creation:

Port 1 can be specified using the reg parameter specifying 0; port 2, 1;
and so on.  The KSZ8794 is a variant of KSZ8795 with port 4 disabled.
So
lan1 = 0, lan2 = 1, lan3 = 2, cpu = 4.
But our company Marketing does not want to promote that fact but treat
KSZ8794 as a distinct product.
So
lan1 = 0, lan2 = 1, lan3 = 2, cpu = 3.
Is this okay to hide this information inside the driver?  This is manageable
for KSZ8794 but for KSZ8864 the first port is disabled:
lan1 = 1, lan2 = 2, lan3 = 3, cpu = 4.

I am not sure whether DSA has or will have a way to display the port
mapping to regular users.