RE: [WARNING: ATTACHMENT UNSCANNED]Re: [PATCH RFC net-next 1/2] net: pcs: xpcs: Add special code to operate in Microchip KSZ9477 switch

[Jose Abreu]

From: Russell King (Oracle) <linux@xxxxxxxxxxxxxxx>
Date: Thu, Jan 30, 2025 at 11:02:00

> On Thu, Jan 30, 2025 at 12:02:27PM +0200, Vladimir Oltean wrote:
> > On Thu, Jan 30, 2025 at 04:50:18AM +0000, Tristram.Ha@xxxxxxxxxxxxx wrote:
> > > This behavior only occurs in KSZ9477 with old IP and so may not reflect
> > > in current specs.  If neg_mode can be set in certain way that disables
> > > auto-negotiation in 1000BASEX mode but enables auto-negotiation in SGMII
> > > mode then this setting is not required.
> > 
> > I see that the KSZ9477 documentation specifies that these bits "must be
> > set to 1 when operating in SerDes mode", but gives no explanation whatsoever,
> > and gives the description of the bits that matches what I see in the
> > XPCS data book (which suggests they would not be needed for 1000Base-X,
> > just for SGMII PHY role).
> 
> Hi Jose,
> 
> Can you help resolve this please?
> 
> Essentially, the KSZ9477 integration of the XPCS hardware used an old
> version of XPCS (we don't know how old). The KSZ9477 documentation
> states that in the AN control register (0x1f8001), buts 4 and 3 must
> be set when operating in "SerDes" mode (aka 1000base-X).
> 
> See page 223 of
> https://urldefense.com/v3/__https://ww1.microchip.com/downloads/aemDocuments/documents/OTH/ProductDocuments/DataSheets/KSZ9477S-Data-Sheet-DS00002392C.pdf__;!!A4F2R9G_pg!d5VxaxYsejdjBjTrDkvz088ikSu1bqS5__YXeLsQoUSIaWwZXCteYOmp6liFtPkRC1s96h5MuhFBjKiYtJ6DPA$ 
> 
> Is this something which the older XPCS hardware version requires?
> 
> Would it be safe to set these two bits with newer XPCS hardware when
> programming it for 1000base-X mode, even though documentation e.g.
> for SJA1105 suggests that these bits do not apply when operating in
> 1000base-X mode?
> 
> Many thanks.

Hi Russell,

Allow me a few days to check internally, I'll get back to you.

Thanks,
Jose