On 9/5/2020 8:53 AM, Paul Barker wrote:
On Sat, 5 Sep 2020 at 16:32, Andrew Lunn <and...@lunn.ch> wrote:
On Sat, Sep 05, 2020 at 03:03:24PM +0100, Paul Barker wrote:
We can't assume that the link partner supports the in-band status
reporting which is enabled by default on the KSZ9893 when using RGMII
for the upstream port.
What do you mean by RGMII inband status reporting? SGMII/1000BaseX has
in band signalling, but RGMII?
Andrew
I'm referencing page 56 of the KSZ9893 datasheet
(http://ww1.microchip.com/downloads/en/DeviceDoc/KSZ9893R-Data-Sheet-DS00002420D.pdf).
The datasheet says "The RGMII port will not function properly if IBS
is enabled in the switch, but it is not receiving in-band status from
a connected PHY." Since we can't guarantee all possible link partners
will support this it should be disabled. In particular, the IMX6 SoC
we're using with this switch doesn't support this on its Ethernet
port.
The RGMII 2.0 specification, pages 7 and 8 has more details:
http://web.archive.org/web/20160303171328/http://www.hp.com/rnd/pdfs/RGMIIv2_0_final_hp.pdf
and section 3.4.1 indicates that this is optional anyway for link
status/speed/duplex.
It comes down to putting a appropriate data word on RXD[7:0] to signal
link status, speed and speed, if the link partner does not provide the
inter-frame word, then the receiver cannot reconstruct that information,
or it will incorrectly decode it.
I don't really know much about how this is implemented or how widely
it's supported.
It is supported by the Broadcom GENET adapter and probably a few others,
however for the same reasons, I have not seen it being widely used. You
would save two reads of BMSR to determine the link status which is nice,
but link parameter changes are disruptive anyway.
--
Florian
