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From: Florian Fainelli <f.fainelli@gmail.com>
To: Paul Barker <pbarker@konsulko.com>, Andrew Lunn <andrew@lunn.ch>
Cc: Woojung Huh <woojung.huh@microchip.com>,
Microchip Linux Driver Support <UNGLinuxDriver@microchip.com>,
Vivien Didelot <vivien.didelot@gmail.com>,
"David S . Miller" <davem@davemloft.net>,
netdev@vger.kernel.org
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: <96496522-3ddd-f8b8-bbc0-63bd29637647@gmail.com> (raw)
In-Reply-To: <CAM9ZRVs8e7hcS4T=Nt6M4iyDWA8uT42m=iRnYzQFg0ajL6rwTw@mail.gmail.com>
On 9/5/2020 8:53 AM, Paul Barker wrote:
> On Sat, 5 Sep 2020 at 16:32, Andrew Lunn <andrew@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
next prev parent 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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