net: stmmac: correct MAC propagation delay

The IEEE1588 Standard specifies that the timestamps of Packets must be
captured when the PTP message timestamp point (leading edge of first
octet after the start of frame delimiter) crosses the boundary between
the node and the network. As the MAC latches the timestamp at an
internal point, the captured timestamp must be corrected for the
additional path latency, as described in the publicly available
datasheet [1].

This patch only corrects for the MAC-Internal delay, which can be read
out from the MAC_Ingress_Timestamp_Latency register, since the Phy
framework currently does not support querying the Phy ingress and egress
latency. The Closs Domain Crossing Circuits errors as indicated in [1]
are already being accounted in the stmmac_get_tx_hwtstamp() function and
are not corrected here.

As the Latency varies for different link speeds and MII
modes of operation, the correction value needs to be updated on each
link state change.

As the delay also causes a phase shift in the timestamp counter compared
to the rest of the network, this correction will also reduce phase error
when generating PPS outputs from the timestamp counter.

[1] i.MX8MP Reference Manual, rev.1 Section 11.7.2.5.3 "Timestamp
correction"

Signed-off-by: Johannes Zink <j.zink@pengutronix.de>
Link: https://lore.kernel.org/r/20230719-stmmac_correct_mac_delay-v2-1-3366f38ee9a6@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ethernet/stmicro/stmmac/hwif.h b/drivers/net/ethernet/stmicro/stmmac/hwif.h
index 652af8f..40147ef 100644 (file)
--- a/drivers/net/ethernet/stmicro/stmmac/hwif.h
+++ b/drivers/net/ethernet/stmicro/stmmac/hwif.h
@@ -532,6 +532,7 @@ struct stmmac_hwtimestamp {
        void (*get_systime) (void __iomem *ioaddr, u64 *systime);
        void (*get_ptptime)(void __iomem *ioaddr, u64 *ptp_time);
        void (*timestamp_interrupt)(struct stmmac_priv *priv);
+       void (*correct_latency)(struct stmmac_priv *priv);
 };
 
 #define stmmac_config_hw_tstamping(__priv, __args...) \
@@ -550,6 +551,8 @@ struct stmmac_hwtimestamp {
        stmmac_do_void_callback(__priv, ptp, get_ptptime, __args)
 #define stmmac_timestamp_interrupt(__priv, __args...) \
        stmmac_do_void_callback(__priv, ptp, timestamp_interrupt, __args)
+#define stmmac_correct_latency(__priv, __args...) \
+       stmmac_do_void_callback(__priv, ptp, correct_latency, __args)
 
 struct stmmac_tx_queue;
 struct stmmac_rx_queue;

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
index fa2c3ba..7e0fa02 100644 (file)
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
@@ -60,6 +60,48 @@ static void config_sub_second_increment(void __iomem *ioaddr,
                *ssinc = data;
 }
 
+static void correct_latency(struct stmmac_priv *priv)
+{
+       void __iomem *ioaddr = priv->ptpaddr;
+       u32 reg_tsic, reg_tsicsns;
+       u32 reg_tsec, reg_tsecsns;
+       u64 scaled_ns;
+       u32 val;
+
+       /* MAC-internal ingress latency */
+       scaled_ns = readl(ioaddr + PTP_TS_INGR_LAT);
+
+       /* See section 11.7.2.5.3.1 "Ingress Correction" on page 4001 of
+        * i.MX8MP Applications Processor Reference Manual Rev. 1, 06/2021
+        */
+       val = readl(ioaddr + PTP_TCR);
+       if (val & PTP_TCR_TSCTRLSSR)
+               /* nanoseconds field is in decimal format with granularity of 1ns/bit */
+               scaled_ns = ((u64)NSEC_PER_SEC << 16) - scaled_ns;
+       else
+               /* nanoseconds field is in binary format with granularity of ~0.466ns/bit */
+               scaled_ns = ((1ULL << 31) << 16) -
+                       DIV_U64_ROUND_CLOSEST(scaled_ns * PSEC_PER_NSEC, 466U);
+
+       reg_tsic = scaled_ns >> 16;
+       reg_tsicsns = scaled_ns & 0xff00;
+
+       /* set bit 31 for 2's compliment */
+       reg_tsic |= BIT(31);
+
+       writel(reg_tsic, ioaddr + PTP_TS_INGR_CORR_NS);
+       writel(reg_tsicsns, ioaddr + PTP_TS_INGR_CORR_SNS);
+
+       /* MAC-internal egress latency */
+       scaled_ns = readl(ioaddr + PTP_TS_EGR_LAT);
+
+       reg_tsec = scaled_ns >> 16;
+       reg_tsecsns = scaled_ns & 0xff00;
+
+       writel(reg_tsec, ioaddr + PTP_TS_EGR_CORR_NS);
+       writel(reg_tsecsns, ioaddr + PTP_TS_EGR_CORR_SNS);
+}
+
 static int init_systime(void __iomem *ioaddr, u32 sec, u32 nsec)
 {
        u32 value;
@@ -221,4 +263,5 @@ const struct stmmac_hwtimestamp stmmac_ptp = {
        .get_systime = get_systime,
        .get_ptptime = get_ptptime,
        .timestamp_interrupt = timestamp_interrupt,
+       .correct_latency = correct_latency,
 };

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index e1f1c03..19e46e8 100644 (file)
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -909,6 +909,8 @@ static int stmmac_init_ptp(struct stmmac_priv *priv)
        priv->hwts_tx_en = 0;
        priv->hwts_rx_en = 0;
 
+       stmmac_correct_latency(priv, priv);
+
        return 0;
 }
 
@@ -1094,6 +1096,8 @@ static void stmmac_mac_link_up(struct phylink_config *config,
 
        if (priv->dma_cap.fpesel)
                stmmac_fpe_link_state_handle(priv, true);
+
+       stmmac_correct_latency(priv, priv);
 }
 
 static const struct phylink_mac_ops stmmac_phylink_mac_ops = {

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.h b/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.h
index bf61929..d1fe4b4 100644 (file)
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.h
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.h
@@ -26,6 +26,12 @@
 #define        PTP_ACR         0x40    /* Auxiliary Control Reg */
 #define        PTP_ATNR        0x48    /* Auxiliary Timestamp - Nanoseconds Reg */
 #define        PTP_ATSR        0x4c    /* Auxiliary Timestamp - Seconds Reg */
+#define        PTP_TS_INGR_CORR_NS     0x58    /* Ingress timestamp correction nanoseconds */
+#define        PTP_TS_EGR_CORR_NS      0x5C    /* Egress timestamp correction nanoseconds*/
+#define        PTP_TS_INGR_CORR_SNS    0x60    /* Ingress timestamp correction subnanoseconds */
+#define        PTP_TS_EGR_CORR_SNS     0x64    /* Egress timestamp correction subnanoseconds */
+#define        PTP_TS_INGR_LAT 0x68    /* MAC internal Ingress Latency */
+#define        PTP_TS_EGR_LAT  0x6c    /* MAC internal Egress Latency */
 
 #define        PTP_STNSUR_ADDSUB_SHIFT 31
 #define        PTP_DIGITAL_ROLLOVER_MODE       0x3B9ACA00      /* 10e9-1 ns */