On 2019-03-16 8:00 pm, Heiko Stuebner wrote:
Am Mittwoch, 13. März 2019, 19:45:36 CET schrieb Peter Geis:
Resubmitting, after further research, review, comments, and suggestions.
Several rk3328 based boards experience high rgmii tx error rates.
This is due to several pins in the rk3328.dtsi rgmii pinmux that are
missing a defined pull strength setting.
This causes the pinmux driver to default to 2ma (bit mask 00).
These pins are only defined in the rk3328.dtsi, and are not listed in
the rk3328 specification.
The TRM only lists them as "Reserved"
(RK3328 TRM V1.1, 3.3.3 Detail Register Description, GRF_GPIO0B_IOMUX,
GRF_GPIO0C_IOMUX, GRF_GPIO0D_IOMUX).
However, removal of these pins from the rgmii pinmux definition causes
the interface to fail to transmit.
Also, the rgmii tx and rx pins defined in the dtsi are not consistent
with the rk3328 specification, with tx pins currently set to 12ma and
rx pins set to 2ma.
Fix this by setting tx pins to 8ma and the rx pins to 4ma, consistent
with the specification.
Defining the drive strength for the undefined pins eliminated the high
tx packet error rate observed under heavy data transfers.
Aligning the drive strength to the TRM values eliminated the occasional
packet retry errors under iperf3 testing.
This allows much higher data rates with no recorded tx errors.
Tested on the rk3328-roc-cc board.
Signed-off-by: Peter Geis <pgwipeout@xxxxxxxxx>
applied as fix for 5.1 after adding Fixes and Cc-stable-tags
FWIW, whilst looking for something else I think I've actually stumbled
across some sort-of-documentation for this mystery pinmux business.
Section 22.5 on p560 of the RK3328 TRM seems to describe IOMUX settings
that line up with the DT snippets from the BSP kernel even though the
GRF section denies them, while Section 22.6.9 on p578 details a wacky
arrangement which at least sheds a little light on that curious "third
mux setting" and why it implies interaction with the
apparently-unconnected internal Tx pads, even if the reasoning behind it
remains rather baffling.
Robin.
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