[PATCH 2/2] ARM: dts: BCM5301X: Set fixed-link for extra Netgear R8000 CPU ports

[Rafał Miłecki]

On 2023-10-16 17:45, Andrew Lunn wrote:
> On Mon, Oct 16, 2023 at 05:36:24PM +0200, Rafał Miłecki wrote:
>> On 2023-10-14 18:50, Andrew Lunn wrote:
>> > On Fri, Oct 13, 2023 at 12:33:14PM +0200, Rafał Miłecki wrote:
>> > > From: Rafał Miłecki <rafal at milecki.pl>
>> > >
>> > > While switch ports 5 and 7 are disabled (vendor designed port 8 to be
>> > > used for CPU traffic) they could be used strictly technically. For
>> > > some
>> > > reason however both those ports need forcing link to be usable.
>> >
>> > This explanation is not making much sense to me.
>> >
>> > I assume this board does not have an RJ45 for these two ports? But
>> > does it have a header so you can access the MII interface?
>> 
>> This PATCH as it is requires a basic familiarity with Northstar 
>> platform
>> or checking bcm-ns.dtsi.
>> 
>> All Northstar (BCM5301X) devices have 3 Ethernet interfaces. 99% of 
>> them
>> have:
>> 1. gmac0 connected to port 5
>> 2. gmac1 connected to port 7
>> 3. gmac2 connected to port 8
>> (it's described in bcm-ns.dtsi).
>> 
>> 
>> Some vendors decide to use gmac0 and switch port 5. They fill NVRAM 
>> with
>> MAC for gmac0.
>> 
>> Some vendors decide to use gmac2 & port 8. They set MAC for gmac2.
>> 
>> 
>> Netgear decided to use gmac2 & port 8 for R8000. They fill NVRAM with
>> MAC for gmac2.
>> 
>> If you however insist on using gmac0 you could do that. That just
>> requires setting up gmac0 with a custom/random MAC and forcing link 
>> for
>> switch ports as described in this PATCH.
> 
> If the ports are not used, you have them set to disabled, why do they
> need a fixed-link? That is what i don't understand yet.

So developers/hackers can use them for custom needs by just dropping
"disabled" bit. That's a pretty simple step compared to figuring out
that a fixed link is needed.

I can imagine advanced users using extra ports and interfaces to get
higher speeds. If you use a single switch port and single interface
you're limited to 1 Gbps. By using two you can exceed that limitation.

This is clearly some corner case but I don't think it really violates
what DT is for. We just describe hardware more clearly. There is a fixed
link after all. That port just happens to be disabled.

-- 
Rafał Miłecki