Revert "net: stmmac: correct MAC propagation delay"

This reverts commit 20bf98c94146eb6fe62177817cb32f53e72dd2e8.

Richard raised concerns about correctness of the code on previous
generations of the HW.

Fixes: 20bf98c94146 ("net: stmmac: correct MAC propagation delay")
Link: https://lore.kernel.org/all/[e-mail]/
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ethernet/stmicro/stmmac/hwif.h

···
 	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...) \
···
 	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;

drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c

···
 		*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;
···
 	.get_systime = get_systime,
 	.get_ptptime = get_ptptime,
 	.timestamp_interrupt = timestamp_interrupt,
-	.correct_latency = correct_latency,
 };

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

···
 	priv->hwts_tx_en = 0;
 	priv->hwts_rx_en = 0;
 
-	stmmac_correct_latency(priv, priv);
-
 	return 0;
 }
 
···
 
 	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 = {

drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.h

···
 #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 */