[PATCH net 1/1] net: stmmac: add fsleep() in HW Rx timestamp checking loop

Tan Tee Min
2022-04-13T03:55:31Z

There is a possibility that the context descriptor still owned by the DMA
even the previous normal descriptor own bit is already cleared. Checking
the context descriptor readiness without delay might be not enough time
for the DMA to update the descriptor field, which causing failure in
getting HW Rx timestamp.

This patch introduces a 1us fsleep() in HW Rx timestamp checking loop
to give time for DMA to update/complete the context descriptor.

ptp4l Timestamp log without this patch:
-----------------------------------------------------------
$ echo 10000 > /sys/class/net/enp0s30f4/gro_flush_timeout
$ echo 10000 > /sys/class/net/enp0s30f4/napi_defer_hard_irqs
$ ptp4l -P2Hi enp0s30f4 --step_threshold=1 -m
ptp4l: selected /dev/ptp2 as PTP clock
ptp4l: port 1: INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l: selected local clock 901210.fffe.b57df7 as best master
ptp4l: port 1: new foreign master 22bb22.fffe.bb22bb-1
ptp4l: selected best master clock 22bb22.fffe.bb22bb
ptp4l: port 1: LISTENING to UNCALIBRATED on RS_SLAVE
ptp4l: port 1: UNCALIBRATED to SLAVE on MASTER_CLOCK_SELECTED
ptp4l: port 1: received SYNC without timestamp
ptp4l: rms 49 max 63 freq -9573 +/- 34 delay 71 +/- 1
ptp4l: rms 15 max 25 freq -9553 +/- 20 delay 72 +/- 0
ptp4l: port 1: received SYNC without timestamp
ptp4l: rms 9 max 18 freq -9540 +/- 11 delay 70 +/- 0
ptp4l: port 1: received PDELAY_REQ without timestamp
ptp4l: rms 16 max 29 freq -9519 +/- 12 delay 72 +/- 0
ptp4l: port 1: received PDELAY_REQ without timestamp
ptp4l: rms 9 max 18 freq -9527 +/- 12 delay 72 +/- 0
ptp4l: rms 5 max 9 freq -9530 +/- 7 delay 70 +/- 0
ptp4l: rms 11 max 20 freq -9530 +/- 16 delay 72 +/- 0
ptp4l: rms 5 max 11 freq -9530 +/- 7 delay 74 +/- 0
ptp4l: rms 6 max 9 freq -9522 +/- 7 delay 72 +/- 0
ptp4l: port 1: received PDELAY_REQ without timestamp
-----------------------------------------------------------

ptp4l Timestamp log with this patch:
-----------------------------------------------------------
$ echo 10000 > /sys/class/net/enp0s30f4/gro_flush_timeout
$ echo 10000 > /sys/class/net/enp0s30f4/napi_defer_hard_irqs
$ ptp4l -P2Hi enp0s30f4 --step_threshold=1 -m
ptp4l: selected /dev/ptp2 as PTP clock
ptp4l: port 1: INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l: selected local clock 901210.fffe.b57df7 as best master
ptp4l: port 1: new foreign master 22bb22.fffe.bb22bb-1
ptp4l: selected best master clock 22bb22.fffe.bb22bb
ptp4l: port 1: LISTENING to UNCALIBRATED on RS_SLAVE
ptp4l: port 1: UNCALIBRATED to SLAVE on MASTER_CLOCK_SELECTED
ptp4l: rms 30 max 45 freq -9400 +/- 23 delay 72 +/- 0
ptp4l: rms 7 max 16 freq -9414 +/- 10 delay 70 +/- 0
ptp4l: rms 6 max 9 freq -9422 +/- 6 delay 72 +/- 0
ptp4l: rms 13 max 20 freq -9436 +/- 13 delay 74 +/- 0
ptp4l: rms 12 max 27 freq -9446 +/- 11 delay 72 +/- 0
ptp4l: rms 9 max 12 freq -9453 +/- 6 delay 74 +/- 0
ptp4l: rms 9 max 15 freq -9438 +/- 11 delay 74 +/- 0
ptp4l: rms 10 max 16 freq -9435 +/- 12 delay 74 +/- 0
ptp4l: rms 8 max 18 freq -9428 +/- 8 delay 72 +/- 0
ptp4l: rms 8 max 18 freq -9423 +/- 8 delay 72 +/- 0
ptp4l: rms 9 max 16 freq -9431 +/- 12 delay 70 +/- 0
ptp4l: rms 9 max 18 freq -9441 +/- 9 delay 72 +/- 0
-----------------------------------------------------------

Fixes: ba1ffd74df74 ("stmmac: fix PTP support for GMAC4")
Cc: <stable@vger.kernel.org> # 5.4.x
Signed-off-by: Song Yoong Siang <yoong.siang.song@intel.com>
Signed-off-by: Tan Tee Min <tee.min.tan@intel.com>
---
drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
index d3b4765c1a5b..289bf26a6105 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
@@ -279,10 +279,11 @@ static int dwmac4_wrback_get_rx_timestamp_status(void *desc, void *next_desc,
/* Check if timestamp is OK from context descriptor */
do {
ret = dwmac4_rx_check_timestamp(next_desc);
- if (ret < 0)
+ if (ret <= 0)
goto exit;
i++;

+ fsleep(1);
} while ((ret == 1) && (i < 10));

if (i == 10)
--
2.25.1