Re: [PATCH net-next v1 1/2] dt-bindings: net: dsa: Add KSZ8567 switch support

[Philippe Schenker]

On Tue, 2024-01-23 at 18:37 +0000, Conor Dooley wrote:
> On Tue, Jan 23, 2024 at 06:30:16PM +0100, Philippe Schenker wrote:
> > 
> > 
> > On Tue, 2024-01-23 at 17:23 +0000, Conor Dooley wrote:
> > > On Tue, Jan 23, 2024 at 05:17:53PM +0100, Philippe Schenker wrote:
> > > > 
> > > > 
> > > > On Tue, 2024-01-23 at 16:06 +0000, Conor Dooley wrote:
> > > > > On Tue, Jan 23, 2024 at 02:50:13PM +0100, Philippe Schenker
> > > > > wrote:
> > > > > > From: Philippe Schenker <philippe.schenker@xxxxxxxxxxxx>
> > > > > > 
> > > > > > This commit adds the dt-binding for KSZ8567, a robust 7-port
> > > > > > Ethernet switch. The KSZ8567 features two RGMII/MII/RMII
> > > > > > interfaces,
> > > > > > each capable of gigabit speeds, complemented by five 10/100
> > > > > > Mbps
> > > > > > MAC/PHYs.
> > > > > > 
> > > > > > Signed-off-by: Philippe Schenker
> > > > > > <philippe.schenker@xxxxxxxxxxxx>
> > > > > 
> > > > > This device has all the same constraints as the other ones in
> > > > > this
> > > > > binding, why is it not compatible with any of them? If it
> > > > > isn't,
> > > > > the
> > > > > compatible should mention why it is not.
> > > > 
> > > > Hi Conor, Thanks for your message!
> > > > 
> > > > I need the compatible to make sure the correct ID of the switch
> > > > is
> > > > being set in the driver as well as its features.
> > > 
> > > Are the features of this switch such that a driver for another ksz
> > > switch would not work (even in a limited capacity) with the 8567?
> > > Things like the register map changing or some feature being
> > > removed
> > > are
> > > examples of why it may not work.
> > 
> > Yes the ksz dsa driver is made so that it checks the ID of the
> > attached
> > chip and refuses to work if it doesn't match. [1]
> 
> That sounds counter productive to be honest. Why does the driver not
> trust that the dt is correct? I saw this recently in some IIO drivers,
> but it was shot down for this sort of reason.
> 
> > It is a very similar chip and uses the same regmap as KSZ9567 but
> > with
> > lower phy-speeds on its 5 switch ports. The two upstream CPU ports
> > are
> > gigabit capable. All this information is set-up in the second patch
> > of
> > this series. [2]
> 
> That, to me, means the lack of a fallback is justified. If it were the
> other way around, then a fallback sounds like it would be suitable.

Yes, I believe a generic fallback would anyway mostly end up with errors
or misbehavior. But I also might be wrong. What I checked is that these
per-switch settings even increased from 5.15..6.7 which to me it seems
those are really needed.
I am no expert in this driver at all I just try to make my hardware work
and with these patches it now seems to switch really well.

> 
> > 
> > I will include a description to the second series. Thanks for your
> > feedback.
> 
> Okay, thanks. You can add
> Acked-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> when you do.
> 
> And despite the email, I have nothing to do with these switches, I am
> just a sucker that signed up to review dt-bindings...

Well, I'm grateful for your review and feedback. Thanks for your work
around Linux kernel! And thanks for the Acked-by.

Philippe

> 
> Thanks,
> Conor.
> 
> > 
> > Philippe
> > 
> > 
> > [1]
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/dsa/microchip/ksz_common.c?h=v6.8-rc1#n3181
> > [2]
> > https://patchwork.kernel.org/project/netdevbpf/patch/20240123135014.614858-2-dev@xxxxxxxxxxxx/
> > 
> > > 
> > > > You mean I shall mention the reason in the commit-message, or
> > > > where?
> > > 
> > > Yes.
> > > 
> > > Thanks,
> > > Conor
> > > 
> > > > > >  Documentation/devicetree/bindings/net/dsa/microchip,ksz.yam
> > > > > > l |
> > > > > > 1 +
> > > > > >  1 file changed, 1 insertion(+)
> > > > > > 
> > > > > > diff --git
> > > > > > a/Documentation/devicetree/bindings/net/dsa/microchip,ksz.ya
> > > > > > ml
> > > > > > b/Documentation/devicetree/bindings/net/dsa/microchip,ksz.ya
> > > > > > ml
> > > > > > index c963dc09e8e1..52acc15ebcbf 100644
> > > > > > ---
> > > > > > a/Documentation/devicetree/bindings/net/dsa/microchip,ksz.ya
> > > > > > ml
> > > > > > +++
> > > > > > b/Documentation/devicetree/bindings/net/dsa/microchip,ksz.ya
> > > > > > ml
> > > > > > @@ -31,6 +31,7 @@ properties:
> > > > > >        - microchip,ksz9893
> > > > > >        - microchip,ksz9563
> > > > > >        - microchip,ksz8563
> > > > > > +      - microchip,ksz8567
> > > > > >  
> > > > > >    reset-gpios:
> > > > > >      description:
> > > > > > -- 
> > > > > > 2.34.1
> > > > > >