Re: [EXT] Re: [PATCH] bus: fsl-mc: Add ACPI support for fsl-mc

[Will Deacon]

On Fri, Jan 31, 2020 at 03:29:06PM +0100, Andrew Lunn wrote:
> > > But by design SFP, SFP+, and QSFP cages are not fixed function network
> > > adapters.  They are physical and logical devices that can adapt to
> > > what is plugged into them.  How the devices are exposed should be
> > > irrelevant to this conversation it is about the underlying
> > > connectivity.
> > 
> > Apologies - I was under the impression that SFP and friends were a
> > physical-layer thing and that a MAC in the SoC would still be fixed such
> > that its DMA and interrupt configuration could be statically described
> > regardless of what transceiver was plugged in (even if some configurations
> > might not use every interrupt/stream ID/etc.) If that isn't the case I shall
> > go and educate myself further.
> 
> It gets interesting with QSFP cages. The Q is quad, there are 4 SERDES
> lanes. You can use them for 1x 40G link, or you can split them into 4x
> 10G links. So you either need one MAC or 4 MACs connecting to the
> cage, and this can change on the fly when a modules is ejected and
> replaced with another module. There are only one set of control pins
> for i2c, loss of signal, TX disable, module inserted. So where the
> interrupt/stream ID/etc are mapped needs some flexibility.
> 
> There is also to some degree a conflict with hiding all this inside
> firmware. This is complex stuff. It is much better to have one core
> implementing in Linux plus some per hardware driver support, than
> having X firmware blobs, generally closed source, each with there own
> bugs which nobody can fix.

Devicetree to the rescue!

Entertaining the use of ACPI without any firmware abstraction for this
hardware really feels like a square peg / round hole situation, so I'm
assuming somebody's telling you that you need it "FOAR ENTAPRYZE". Who
is it and can you tell them to bog off?

Will