linux-kernel - Re: [RFC PATCH net v2 0/3] Fix OdroidC2 Gigabit Tx link issue

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Date:   Thu, 24 Nov 2016 15:40:51 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Jerome Brunet <jbrunet@...libre.com>
Cc:     netdev@...r.kernel.org, devicetree@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Carlo Caione <carlo@...one.org>,
        Kevin Hilman <khilman@...libre.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        Andre Roth <neolynx@...il.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH net v2 0/3] Fix OdroidC2 Gigabit Tx link issue

Hi Jerome,

On Mon, Nov 21, 2016 at 4:35 PM, Jerome Brunet <jbrunet@...libre.com> wrote:
> This patchset fixes an issue with the OdroidC2 board (DWMAC + RTL8211F).
> Initially reported as a low Tx throughput issue at gigabit speed, the
> platform enters LPI too often. This eventually break the link (both Tx
> and Rx), and require to bring the interface down and up again to get the
> Rx path working again.
>
> The root cause of this issue is not fully understood yet but disabling EEE
> advertisement on the PHY prevent this feature to be negotiated.
> With this change, the link is stable and reliable, with the expected
> throughput performance.
I have just sent a series which allows configuring the TX delay on the
MAC (dwmac-meson8b glue) side: [0]
Disabling the TX delay generated by the MAC fixes TX throughput for
me, even when leaving EEE enabled in the RTL8211F PHY driver!

Unfortunately the RTL8211F PHY is a black-box for the community
because there is no public datasheeet available.
*maybe* (pure speculation!) they're enabling the TX delay based on
some internal magic only when EEE is enabled.

Jerome, could you please re-test the behavior on your Odroid-C2 when
you have EEE still enabled but the TX-delay disabled?
In my case throughput is fine, and "$ ethtool -S eth0 | grep lpi" gives:
    irq_tx_path_in_lpi_mode_n: 0
    irq_tx_path_exit_lpi_mode_n: 0
    irq_rx_path_in_lpi_mode_n: 0
    irq_rx_path_exit_lpi_mode_n: 0


Regards,
Martin


[0] http://lists.infradead.org/pipermail/linux-amlogic/2016-November/001674.html