From: Voon Weifeng <[email protected]>
According to Synopsis DesignWare EQoS Databook, the Clock Domain Cross
synchronization error is introduced tue to the clock(GMII Tx/Rx clock)
being different at the capture as compared to the PTP
clock(clk_ptp_ref_i) that is used to generate the time.
The CDC synchronization error is almost equal to 2 times the clock
period of the PTP clock(clk_ptp_ref_i).
On a Intel Tigerlake platform (with Marvell 88E2110 external PHY):
Before applying this patch (with CDC synchronization error):
ptp4l[64.044]: rms 8 max 13 freq +30877 +/- 11 delay 216 +/- 0
ptp4l[65.047]: rms 13 max 20 freq +30869 +/- 17 delay 213 +/- 0
ptp4l[66.050]: rms 12 max 20 freq +30857 +/- 11 delay 213 +/- 0
ptp4l[67.052]: rms 11 max 22 freq +30849 +/- 10 delay 215 +/- 0
ptp4l[68.055]: rms 10 max 16 freq +30853 +/- 13 delay 215 +/- 0
ptp4l[69.057]: rms 7 max 13 freq +30848 +/- 9 delay 216 +/- 0
ptp4l[70.060]: rms 8 max 13 freq +30846 +/- 10 delay 216 +/- 0
ptp4l[71.063]: rms 9 max 15 freq +30836 +/- 8 delay 218 +/- 0
After applying this patch (CDC syncrhonization error is taken care of):
ptp4l[61.516]: rms 773 max 824 freq +31526 +/- 158 delay 200 +/- 0
ptp4l[62.519]: rms 427 max 596 freq +31668 +/- 39 delay 198 +/- 0
ptp4l[63.522]: rms 113 max 206 freq +31482 +/- 57 delay 198 +/- 0
ptp4l[64.525]: rms 40 max 56 freq +31316 +/- 29 delay 200 +/- 0
ptp4l[65.528]: rms 47 max 56 freq +31255 +/- 17 delay 200 +/- 0
ptp4l[66.531]: rms 26 max 36 freq +31246 +/- 9 delay 200 +/- 0
ptp4l[67.534]: rms 12 max 18 freq +31254 +/- 12 delay 202 +/- 0
ptp4l[68.537]: rms 7 max 12 freq +31263 +/- 10 delay 202 +/- 0
Signed-off-by: Voon Weifeng <[email protected]>
Signed-off-by: Wong Vee Khee <[email protected]>
---
.../net/ethernet/stmicro/stmmac/stmmac_main.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index a10704d8e3c6..ddf54b8ad75d 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -466,6 +466,7 @@ static void stmmac_get_tx_hwtstamp(struct stmmac_priv *priv,
{
struct skb_shared_hwtstamps shhwtstamp;
bool found = false;
+ s64 adjust = 0;
u64 ns = 0;
if (!priv->hwts_tx_en)
@@ -484,6 +485,13 @@ static void stmmac_get_tx_hwtstamp(struct stmmac_priv *priv,
}
if (found) {
+ /* Correct the clk domain crossing(CDC) error */
+ if (priv->plat->has_gmac4 && priv->plat->clk_ptp_rate) {
+ adjust += -(2 * (NSEC_PER_SEC /
+ priv->plat->clk_ptp_rate));
+ ns += adjust;
+ }
+
memset(&shhwtstamp, 0, sizeof(struct skb_shared_hwtstamps));
shhwtstamp.hwtstamp = ns_to_ktime(ns);
@@ -507,6 +515,7 @@ static void stmmac_get_rx_hwtstamp(struct stmmac_priv *priv, struct dma_desc *p,
{
struct skb_shared_hwtstamps *shhwtstamp = NULL;
struct dma_desc *desc = p;
+ u64 adjust = 0;
u64 ns = 0;
if (!priv->hwts_rx_en)
@@ -518,6 +527,13 @@ static void stmmac_get_rx_hwtstamp(struct stmmac_priv *priv, struct dma_desc *p,
/* Check if timestamp is available */
if (stmmac_get_rx_timestamp_status(priv, p, np, priv->adv_ts)) {
stmmac_get_timestamp(priv, desc, priv->adv_ts, &ns);
+
+ /* Correct the clk domain crossing(CDC) error */
+ if (priv->plat->has_gmac4 && priv->plat->clk_ptp_rate) {
+ adjust += 2 * (NSEC_PER_SEC / priv->plat->clk_ptp_rate);
+ ns -= adjust;
+ }
+
netdev_dbg(priv->dev, "get valid RX hw timestamp %llu\n", ns);
shhwtstamp = skb_hwtstamps(skb);
memset(shhwtstamp, 0, sizeof(struct skb_shared_hwtstamps));
--
2.25.1
Hello:
This patch was applied to netdev/net-next.git (refs/heads/master):
On Wed, 17 Mar 2021 12:09:04 +0800 you wrote:
> From: Voon Weifeng <[email protected]>
>
> According to Synopsis DesignWare EQoS Databook, the Clock Domain Cross
> synchronization error is introduced tue to the clock(GMII Tx/Rx clock)
> being different at the capture as compared to the PTP
> clock(clk_ptp_ref_i) that is used to generate the time.
>
> [...]
Here is the summary with links:
- [net-next,1/1] net: stmmac: add timestamp correction to rid CDC sync error
https://git.kernel.org/netdev/net-next/c/3600be5f58c1
You are awesome, thank you!
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