[RFC,v1,0/2] dwmac-meson8b Ethernet RX delay configuration

Message

Martin Blumenstingl Dec. 26, 2019, 8:36 p.m. UTC

The Ethernet TX performance has been historically bad on Meson8b and
Meson8m2 SoCs because high packet loss was seen. I found out that this
was related (yet again) to the RGMII TX delay configuration.
In the process of discussing the big picture (and not just a single
patch) [0] with Andrew I discovered that the IP block behind the
dwmac-meson8b driver actually seems to support the configuration of the
RGMII RX delay (at least on the Meson8b SoC generation).

The goal of this series is to start the discussion around how to
implement the RGMII RX delay on this IP block. Additionally it seems
that the RX delay can also be applied for RMII PHYs?

@Jianxin: can you please add the Amlogic internal Ethernet team to this
discussion? My questions are documented in the patch description of
patch #2.

Dependencies: this series is based on my other series [1]
"net: stmmac: dwmac-meson8b: Fix the RGMII TX delay on Meson8b/8m2 SoCs"


@David: please do NOT merge this series yet, it's only meant for
discussion in it's current state!


[0] https://patchwork.kernel.org/patch/11309891/
[1] https://patchwork.kernel.org/patch/11310669/


Martin Blumenstingl (2):
  net: stmmac: dwmac-meson8b: use FIELD_PREP instead of open-coding it
  net: stmmac: dwmac-meson8b: add support for the RX delay configuration

 .../ethernet/stmicro/stmmac/dwmac-meson8b.c   | 60 ++++++++++---------
 1 file changed, 33 insertions(+), 27 deletions(-)

Comments

Martin Blumenstingl Jan. 7, 2020, 2:01 p.m. UTC | #1

Hello Jianxin,

On Thu, Dec 26, 2019 at 9:37 PM Martin Blumenstingl
<[e-mail]> wrote:
>
> The Ethernet TX performance has been historically bad on Meson8b and
> Meson8m2 SoCs because high packet loss was seen. I found out that this
> was related (yet again) to the RGMII TX delay configuration.
> In the process of discussing the big picture (and not just a single
> patch) [0] with Andrew I discovered that the IP block behind the
> dwmac-meson8b driver actually seems to support the configuration of the
> RGMII RX delay (at least on the Meson8b SoC generation).
>
> The goal of this series is to start the discussion around how to
> implement the RGMII RX delay on this IP block. Additionally it seems
> that the RX delay can also be applied for RMII PHYs?
>
> @Jianxin: can you please add the Amlogic internal Ethernet team to this
> discussion? My questions are documented in the patch description of
> patch #2.
do you already have an update for me on this topic?

while we're discussing unknown bits of the Ethernet controller I also
remembered that we're currently not describing the relation between
the "fclk_div2" clock and the Ethernet controller. however, as
described in commit 72e1f230204039 ("clk: meson: meson8b: mark
fclk_div2 gate clocks as CLK_IS_CRITICAL") this is needed for RGMII
mode.
it would be great to know the relation between fclk_div2 and RGMII
mode on the Ethernet controller!


Thank you!
Martin