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net: stmmac: Calculate CDC error only once

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The clock domain crossing error (CDC) is calculated at every fetch of Tx or Rx
timestamps. It includes a division. Especially on arm32 based systems it is
expensive. It also requires two conditionals in the hotpath.

Add a compensation value cache to struct plat_stmmacenet_data and subtract it
unconditionally in the RX/TX functions which spares the conditionals.

The value is initialized to 0 and if supported calculated in the PTP
initialization code.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Link: https://lore.kernel.org/r/20211122111931.135135-1-kurt@linutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Kurt Kanzenbach 2021-11-22 12:19:31 +01:00 committed by Jakub Kicinski
parent 2106efda78
commit c6d5f19330
3 changed files with 8 additions and 10 deletions
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12
drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
View file

@ -511,14 +511,6 @@ bool stmmac_eee_init(struct stmmac_priv *priv)
return true;
}
static inline u32 stmmac_cdc_adjust(struct stmmac_priv *priv)
{
/* Correct the clk domain crossing(CDC) error */
if (priv->plat->has_gmac4 && priv->plat->clk_ptp_rate)
return (2 * NSEC_PER_SEC) / priv->plat->clk_ptp_rate;
return 0;
}
/* stmmac_get_tx_hwtstamp - get HW TX timestamps
* @priv: driver private structure
* @p : descriptor pointer
@ -550,7 +542,7 @@ static void stmmac_get_tx_hwtstamp(struct stmmac_priv *priv,
}
if (found) {
ns -= stmmac_cdc_adjust(priv);
ns -= priv->plat->cdc_error_adj;
memset(&shhwtstamp, 0, sizeof(struct skb_shared_hwtstamps));
shhwtstamp.hwtstamp = ns_to_ktime(ns);
@ -587,7 +579,7 @@ static void stmmac_get_rx_hwtstamp(struct stmmac_priv *priv, struct dma_desc *p,
if (stmmac_get_rx_timestamp_status(priv, p, np, priv->adv_ts)) {
stmmac_get_timestamp(priv, desc, priv->adv_ts, &ns);
ns -= stmmac_cdc_adjust(priv);
ns -= priv->plat->cdc_error_adj;
netdev_dbg(priv->dev, "get valid RX hw timestamp %llu\n", ns);
shhwtstamp = skb_hwtstamps(skb);

5
drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c
View file

@ -309,6 +309,11 @@ void stmmac_ptp_register(struct stmmac_priv *priv)
if (priv->plat->ptp_max_adj)
stmmac_ptp_clock_ops.max_adj = priv->plat->ptp_max_adj;
/* Calculate the clock domain crossing (CDC) error if necessary */
priv->plat->cdc_error_adj = 0;
if (priv->plat->has_gmac4 && priv->plat->clk_ptp_rate)
priv->plat->cdc_error_adj = (2 * NSEC_PER_SEC) / priv->plat->clk_ptp_rate;
stmmac_ptp_clock_ops.n_per_out = priv->dma_cap.pps_out_num;
stmmac_ptp_clock_ops.n_ext_ts = priv->dma_cap.aux_snapshot_n;

1
include/linux/stmmac.h
View file

@ -241,6 +241,7 @@ struct plat_stmmacenet_data {
unsigned int clk_ref_rate;
unsigned int mult_fact_100ns;
s32 ptp_max_adj;
u32 cdc_error_adj;
struct reset_control *stmmac_rst;
struct reset_control *stmmac_ahb_rst;
struct stmmac_axi *axi;