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From: Florian Fainelli <>
To: Paul Barker <>, Andrew Lunn <>
Cc: Woojung Huh <>,
	Microchip Linux Driver Support <>,
	Vivien Didelot <>,
	"David S . Miller" <>,
Subject: Re: [PATCH 3/4] net: dsa: microchip: Disable RGMII in-band status on KSZ9893
Date: Sat, 5 Sep 2020 09:04:59 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 9/5/2020 8:53 AM, Paul Barker wrote:
> On Sat, 5 Sep 2020 at 16:32, Andrew Lunn <> 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
> (
> 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:

and section 3.4.1 indicates that this is optional anyway for link 

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.

  reply	other threads:[~2020-09-05 16:05 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-05 14:03 [PATCH 0/4] ksz9477 dsa switch driver improvements Paul Barker
2020-09-05 14:03 ` [PATCH 1/4] net: dsa: microchip: Make switch detection more informative Paul Barker
2020-09-05 15:28   ` Andrew Lunn
2020-09-05 14:03 ` [PATCH 2/4] net: dsa: microchip: Add debug print for XMII port mode Paul Barker
2020-09-05 15:31   ` Andrew Lunn
2020-09-05 14:03 ` [PATCH 3/4] net: dsa: microchip: Disable RGMII in-band status on KSZ9893 Paul Barker
2020-09-05 15:32   ` Andrew Lunn
2020-09-05 15:53     ` Paul Barker
2020-09-05 16:04       ` Florian Fainelli [this message]
2020-09-05 16:06       ` Andrew Lunn
2020-09-05 14:03 ` [PATCH 4/4] net: dsa: microchip: Implement recommended reset timing Paul Barker
2020-09-05 15:34 ` [PATCH 0/4] ksz9477 dsa switch driver improvements Andrew Lunn
2020-09-05 15:54   ` Paul Barker

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