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

-----Original Message-----
From: Andrew Lunn [mailto:andrew@lunn.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@vger.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:

quoted

2017-09-08 0:54 GMT+03:00 Andrew Lunn [off-list ref]:

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-- compatible: For external switch chips, compatible string must be exactly

one

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-  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.