Re: [net-next PATCH v1 0/2] stmmac: dwmac-meson8b: configurable RGMII TX delay

On Thu, 2016-11-24 at 18:05 +0100, Martin Blumenstingl wrote:

On Thu, Nov 24, 2016 at 4:56 PM, Jerome Brunet [off-list ref]
wrote:

quoted

On Thu, 2016-11-24 at 15:34 +0100, Martin Blumenstingl wrote:

quoted

Currently the dwmac-meson8b stmmac glue driver uses a hardcoded
1/4
cycle TX clock delay. This seems to work fine for many boards
(for
example Odroid-C2 or Amlogic's reference boards) but there are
some
others where TX traffic is simply broken.
There are probably multiple reasons why it's working on some
boards
while it's broken on others:
- some of Amlogic's reference boards are using a Micrel PHY
- hardware circuit design
- maybe more...

This raises a question though:
Which device is supposed to enable the TX delay when both MAC and
PHY
support it? And should we implement it for each PHY / MAC
separately
or should we think about a more generic solution (currently it's
not
possible to disable the TX delay generated by the RTL8211F PHY
via
devicetree when using phy-mode "rgmii")?

Actually you can skip the part which activate the Tx-delay on the
phy
by setting "phy-mode = "rgmii-id" instead of "rgmii"

phy->interface will no longer be PHY_INTERFACE_MODE_RGMII
but PHY_INTERFACE_MODE_RGMII_ID.

unfortunately this is not true for RTL8211F (I did my previous tests
with the same expectation in mind)!
the code seems to suggest that TX-delay is disabled whenever mode !=
PHY_INTERFACE_MODE_RGMII.
BUT: on my device RTL8211F_TX_DELAY is set even before
"phy_write(phydev, 0x11, reg);"!

Thx a lot for pointing this out. I wrongly assumed that is was off by
default. It turns out it is ON on the OdroidC2 as well.

So I re-did all my test:
On the OdroidC2, as long as eee is not disabled (using ethtool or
through my patch) I can't get iperf to work properly. Disabling EEE,
the link works for the following configurations:

PHY TX Delay bit set : MAC delay 0ns, 2ns.
PHY TX Delay bit cleared : MAC delay 2ns, 4ns.

This seems to confirm that the PHY adds a 2ns delay when the bit is
set.

I could not test on my MXQPRO2.1 ... the PHY is no longer found during
the boot. Something died overnight :( 

Based on what I found it seems that rgmii-id, rgmii-txid and
rgmii-rxid are supposed to be handled by the PHY.
That would mean that we have two problems here:
1) drivers/net/phy/realtek.c:rtl8211f_config_init should check for
PHY_INTERFACE_MODE_RGMII_ID or PHY_INTERFACE_MODE_RGMII_TXID and
enable the TX-delay in that case - otherwise explicitly disable it
2) dwmac-meson8b.c should only use the configured TX-delay for
PHY_INTERFACE_MODE_RGMII
@Florian: could you please share your thoughts on this (who handles
the TX delay in which case)?


Regards,
Martin

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