| Message ID | 20200905140325.108846-4-pbarker@konsulko.com |
|---|---|
| State | Changes Requested |
| Delegated to: | David Miller |
| Headers | show |
| Series | ksz9477 dsa switch driver improvements | expand |
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
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. I don't really know much about how this is implemented or how widely it's supported. Thanks,
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.
On Sat, Sep 05, 2020 at 04:53:20PM +0100, 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. > > I don't really know much about how this is implemented or how widely > it's supported. I never knew RGMII had this. What i did find was: http://web.archive.org/web/20160303171328/http://www.hp.com/rnd/pdfs/RGMIIv2_0_final_hp.pdf which does talk about it, section 3.4.1. It is clearly optional, and since this is the first time i've heard of it, i suspect not many systems actually implement it. So turning it off seems wise. Reviewed-by: Andrew Lunn <andrew@lunn.ch> Andrew
diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c index 3e36aa628c9f..2c953ab6ce16 100644 --- a/drivers/net/dsa/microchip/ksz9477.c +++ b/drivers/net/dsa/microchip/ksz9477.c @@ -1240,6 +1240,9 @@ static void ksz9477_port_setup(struct ksz_device *dev, int port, bool cpu_port) if (dev->interface == PHY_INTERFACE_MODE_RGMII_ID || dev->interface == PHY_INTERFACE_MODE_RGMII_TXID) data8 |= PORT_RGMII_ID_EG_ENABLE; + /* On KSZ9893, disable RGMII in-band status support */ + if (dev->features & IS_9893) + data8 &= ~PORT_MII_MAC_MODE; p->phydev.speed = SPEED_1000; break; }
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. Signed-off-by: Paul Barker <pbarker@konsulko.com> --- drivers/net/dsa/microchip/ksz9477.c | 3 +++ 1 file changed, 3 insertions(+)