Re: [PATCH 5/5] ARM: dts: BCM5301X: Disable unused gmac0 and gmac2 on Asus RT-AC88U

["Arınç ÜNAL" <arinc.unal@arinc9.com>]

On 01/04/2022 13:40, Rafał Miłecki wrote:
> On 2022-04-01 12:20, Arınç ÜNAL wrote:
>> Disable gmac0 and gmac2 which are currently not used. This doesn't 
>> seem to
>> be implemented yet on drivers/net/ethernet/broadcom/bgmac-bcma.c but this
>> change is harmless, nonetheless.
> 
> It doesn't matter whether Linux respects that.
> 
> 
>> Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
>> ---
>>  arch/arm/boot/dts/bcm47094-asus-rt-ac88u.dts | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/arch/arm/boot/dts/bcm47094-asus-rt-ac88u.dts
>> b/arch/arm/boot/dts/bcm47094-asus-rt-ac88u.dts
>> index 2f944d1c0330..0f5c5d576814 100644
>> --- a/arch/arm/boot/dts/bcm47094-asus-rt-ac88u.dts
>> +++ b/arch/arm/boot/dts/bcm47094-asus-rt-ac88u.dts
>> @@ -242,11 +242,19 @@ fixed-link {
>>      };
>>  };
>>
>> +&gmac0 {
>> +    status = "disabled";
>> +};
>> +
>>  &gmac1 {
>>      nvmem-cells = <&et1macaddr>;
>>      nvmem-cell-names = "mac-address";
>>  };
>>
>> +&gmac2 {
>> +    status = "disabled";
>> +};
> 
> I don't think that is correct. Those interfaces are still there and
> they are actually connected to switch ports. If you configure your
> switch properly you can use them.
> 
> Someone may want to use e.g. gmac0 & gmac1 with two sets of ports to
> speed up network communication.
> 
> I think gmac2 is required if you want to enable FA (flow acceleration /
> accelerator) - even though there isn't Linux driver for it yet.
> 
> They are not disabled / unpopulated / non functional interfaces.

I understand your point. However, while we're not supposed to care 
whether the kernel respects the bindings, don't we also need to make the 
bindings work on the version of the Linux kernel we're submitting the 
bindings to?

With the current way DSA works, only one switch port can be used as a 
CPU port. If we were to remove the status = "disabled" property from 
port@8 which connects to gmac2, it'd break the communication between the 
switch and the CPU on the current Linux kernel.

If a new driver or a feature is introduced, we should update the 
bindings accordingly afterwards.

For this reason, I don't see an issue with explaining the driver side of 
it on the commit log for DT bindings.

DT bindings are not exactly static either. Someone could want to use 
gmac2 instead of gmac1. In that case, I think they should change the 
bindings themselves as it's for their own use.

By the way, gmac0 would be wired to port@5 but since port@5 is wired to 
realtek switch's port@6 instead, it's actually non-functional.

Arınç