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From:   Johannes Zink <j.zink@pengutronix.de>
Date:   Tue, 01 Aug 2023 17:44:29 +0200
Subject: [PATCH v3 1/2] net: stmmac: correct MAC propagation delay
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Message-Id: <20230719-stmmac_correct_mac_delay-v3-1-61e63427735e@pengutronix.de>
References: <20230719-stmmac_correct_mac_delay-v3-0-61e63427735e@pengutronix.de>
In-Reply-To: <20230719-stmmac_correct_mac_delay-v3-0-61e63427735e@pengutronix.de>
To:     Giuseppe Cavallaro <peppe.cavallaro@st.com>,
        Alexandre Torgue <alexandre.torgue@foss.st.com>,
        Jose Abreu <joabreu@synopsys.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Richard Cochran <richardcochran@gmail.com>,
        Russell King <linux@armlinux.org.uk>
Cc:     patchwork-jzi@pengutronix.de, netdev@vger.kernel.org,
        linux-stm32@st-md-mailman.stormreply.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        kernel@pengutronix.de, Kurt Kanzenbach <kurt@linutronix.de>,
        kernel test robot <lkp@intel.com>,
        Johannes Zink <j.zink@pengutronix.de>
Precedence: bulk

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 data transmission 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 on DWMAC version 5,
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.

Since the correction registers may be unavailable on some hardware and
no feature bits are documented for dynamically detection of the MAC
propagation delay readout, introduce a feature bit to explicitely enable
MAC delay Correction in the gluecode driver.

[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

---

Changes in v3:
  - worked in Richard's review findings. Thank your for your review:
    - don't do the correction unconditionally, since the correction
      registers are not guaranteed to be available on any hardware
  - refactored function names to better reflect the functionality
  - clarified commit message
Changes in v2:
  - fix builds for 32bit, this was found by the kernel build bot
	Reported-by: kernel test robot <lkp@intel.com>
	Closes:
	https://lore.kernel.org/oe-kbuild-all/202307200225.B8rmKQPN-lkp@intel.com/
  - while at it also fix an overflow by shifting a u32 constant from macro by 10bits
    by casting the constant to u64
---
 drivers/net/ethernet/stmicro/stmmac/hwif.h         |  3 ++
 .../net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c  | 43 ++++++++++++++++++++++
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c  |  6 +++
 drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.h   |  6 +++
 include/linux/stmmac.h                             |  1 +
 5 files changed, 59 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/hwif.h b/drivers/net/ethernet/stmicro/stmmac/hwif.h
index 652af8f6e75f..238f17c50a1e 100644
--- 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 (*hwtstamp_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_hwtstamp_correct_latency(__priv, __args...) \
+	stmmac_do_void_callback(__priv, ptp, hwtstamp_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 fa2c3ba7e9fe..540f6a4ec0b8 100644
--- 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 hwtstamp_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,
+	.hwtstamp_correct_latency = hwtstamp_correct_latency,
 };
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index e1f1c034d325..99aa5360b3ff 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -909,6 +909,9 @@ static int stmmac_init_ptp(struct stmmac_priv *priv)
 	priv->hwts_tx_en = 0;
 	priv->hwts_rx_en = 0;
 
+	if (priv->plat->flags & STMMAC_FLAG_HWTSTAMP_CORRECT_LATENCY)
+		stmmac_hwtstamp_correct_latency(priv, priv);
+
 	return 0;
 }
 
@@ -1094,6 +1097,9 @@ static void stmmac_mac_link_up(struct phylink_config *config,
 
 	if (priv->dma_cap.fpesel)
 		stmmac_fpe_link_state_handle(priv, true);
+
+	if (priv->plat->flags & STMMAC_FLAG_HWTSTAMP_CORRECT_LATENCY)
+		stmmac_hwtstamp_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 bf619295d079..d1fe4b46f162 100644
--- 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 */
diff --git a/include/linux/stmmac.h b/include/linux/stmmac.h
index 3d0702510224..652404c03944 100644
--- a/include/linux/stmmac.h
+++ b/include/linux/stmmac.h
@@ -218,6 +218,7 @@ struct dwmac4_addrs {
 #define STMMAC_FLAG_INT_SNAPSHOT_EN		BIT(9)
 #define STMMAC_FLAG_RX_CLK_RUNS_IN_LPI		BIT(10)
 #define STMMAC_FLAG_EN_TX_LPI_CLOCKGATING	BIT(11)
+#define STMMAC_FLAG_HWTSTAMP_CORRECT_LATENCY	BIT(12)
 
 struct plat_stmmacenet_data {
 	int bus_id;

-- 
2.39.2