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Message-Id: <20250625124127.4176960-1-o.rempel@pengutronix.de>
Date: Wed, 25 Jun 2025 14:41:26 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Andrew Lunn <andrew@...n.ch>,
Heiner Kallweit <hkallweit1@...il.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>,
kernel@...gutronix.de,
linux-kernel@...r.kernel.org,
Russell King <linux@...linux.org.uk>,
netdev@...r.kernel.org
Subject: [PATCH net-next v2 1/1] phy: micrel: add Signal Quality Indicator (SQI) support for KSZ9477 switch PHYs
Add support for the Signal Quality Index (SQI) feature on KSZ9477 family
switches. This feature provides a relative measure of receive signal
quality.
The KSZ9477 PHY provides four separate SQI values for a 1000BASE-T link,
one for each differential pair (Channel A-D). Since the current get_sqi
UAPI only supports returning a single value per port, this
implementation reads the SQI from Channel A as a representative metric.
This can be extended to provide per-channel readings once the UAPI is
enhanced for multi-channel support.
The hardware provides a raw 7-bit SQI value (0-127), where lower is
better. This raw value is converted to the standard 0-7 scale to provide
a usable, interoperable metric for userspace tools, abstracting away
hardware-specifics. The mapping to the standard 0-7 SQI scale was
determined empirically by injecting a 30MHz sine wave into the receive
pair with a signal generator. It was observed that the link becomes
unstable and drops when the raw SQI value reaches 8. This
implementation is based on these test results.
Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
changes v2:
- Reword commit message
- Fix SQI value inversion
- Implement an empirically-derived, non-linear mapping to the standard
0-7 SQI scale
---
drivers/net/phy/micrel.c | 124 +++++++++++++++++++++++++++++++++++++++
1 file changed, 124 insertions(+)
diff --git a/drivers/net/phy/micrel.c b/drivers/net/phy/micrel.c
index d0429dc8f561..6422d9a7c09f 100644
--- a/drivers/net/phy/micrel.c
+++ b/drivers/net/phy/micrel.c
@@ -2173,6 +2173,128 @@ static void kszphy_get_phy_stats(struct phy_device *phydev,
stats->rx_errors = priv->phy_stats.rx_err_pkt_cnt;
}
+/* Base register for Signal Quality Indicator (SQI) - Channel A
+ *
+ * MMD Address: MDIO_MMD_PMAPMD (0x01)
+ * Register: 0xAC (Channel A)
+ * Each channel (pair) has its own register:
+ * Channel A: 0xAC
+ * Channel B: 0xAD
+ * Channel C: 0xAE
+ * Channel D: 0xAF
+ */
+#define KSZ9477_MMD_SIGNAL_QUALITY_CHAN_A 0xAC
+
+/* SQI field mask for bits [14:8]
+ *
+ * SQI indicates relative quality of the signal.
+ * A lower value indicates better signal quality.
+ */
+#define KSZ9477_MMD_SQI_MASK GENMASK(14, 8)
+
+#define KSZ9477_SQI_MAX 7
+
+/* Delay between consecutive SQI register reads in microseconds.
+ *
+ * Reference: KSZ9477S Datasheet DS00002392C, Section 4.1.11 (page 26)
+ * The register is updated every 2 µs. Use 3 µs to avoid redundant reads.
+ */
+#define KSZ9477_MMD_SQI_READ_DELAY_US 3
+
+/* Number of SQI samples to average for a stable result.
+ *
+ * Reference: KSZ9477S Datasheet DS00002392C, Section 4.1.11 (page 26)
+ * For noisy environments, a minimum of 30–50 readings is recommended.
+ */
+#define KSZ9477_SQI_SAMPLE_COUNT 40
+
+/* The hardware SQI register provides a raw value from 0-127, where a lower
+ * value indicates better signal quality. However, empirical testing has
+ * shown that only the 0-7 range is relevant for a functional link. A raw
+ * value of 8 or higher was measured directly before link drop. This aligns
+ * with the OPEN Alliance recommendation that SQI=0 should represent the
+ * pre-failure state.
+ *
+ * This table provides a non-linear mapping from the useful raw hardware
+ * values (0-7) to the standard 0-7 SQI scale, where higher is better.
+ */
+static const u8 ksz_sqi_mapping[] = {
+ 7, /* raw 0 -> SQI 7 */
+ 7, /* raw 1 -> SQI 7 */
+ 6, /* raw 2 -> SQI 6 */
+ 5, /* raw 3 -> SQI 5 */
+ 4, /* raw 4 -> SQI 4 */
+ 3, /* raw 5 -> SQI 3 */
+ 2, /* raw 6 -> SQI 2 */
+ 1, /* raw 7 -> SQI 1 */
+};
+
+/**
+ * kszphy_get_sqi - Read, average, and map Signal Quality Index (SQI)
+ * @phydev: the PHY device
+ *
+ * This function reads and processes the raw Signal Quality Index from the
+ * PHY. Based on empirical testing, a raw value of 8 or higher indicates a
+ * pre-failure state and is mapped to SQI 0. Raw values from 0-7 are
+ * mapped to the standard 0-7 SQI scale via a lookup table.
+ *
+ * Return: SQI value (0–7), or a negative errno on failure.
+ */
+static int kszphy_get_sqi(struct phy_device *phydev)
+{
+ int sum = 0;
+ int i, val, raw_sqi, avg_raw_sqi;
+ u8 channels;
+
+ /* Determine applicable channels based on link speed */
+ if (phydev->speed == SPEED_1000)
+ /* TODO: current SQI API only supports 1 channel. */
+ channels = 1;
+ else if (phydev->speed == SPEED_100)
+ channels = 1;
+ else
+ return -EOPNOTSUPP;
+
+ /*
+ * Sample and accumulate SQI readings for each pair (currently only one).
+ *
+ * Reference: KSZ9477S Datasheet DS00002392C, Section 4.1.11 (page 26)
+ * - The SQI register is updated every 2 µs.
+ * - Values may fluctuate significantly, even in low-noise environments.
+ * - For reliable estimation, average a minimum of 30–50 samples
+ * (recommended for noisy environments)
+ * - In noisy environments, individual readings are highly unreliable.
+ *
+ * We use 40 samples per pair with a delay of 3 µs between each
+ * read to ensure new values are captured (2 µs update interval).
+ */
+ for (i = 0; i < KSZ9477_SQI_SAMPLE_COUNT; i++) {
+ val = phy_read_mmd(phydev, MDIO_MMD_PMAPMD,
+ KSZ9477_MMD_SIGNAL_QUALITY_CHAN_A);
+ if (val < 0)
+ return val;
+
+ raw_sqi = FIELD_GET(KSZ9477_MMD_SQI_MASK, val);
+ sum += raw_sqi;
+
+ udelay(KSZ9477_MMD_SQI_READ_DELAY_US);
+ }
+
+ avg_raw_sqi = sum / KSZ9477_SQI_SAMPLE_COUNT;
+
+ /* Handle the pre-fail/failed state first. */
+ if (avg_raw_sqi >= ARRAY_SIZE(ksz_sqi_mapping))
+ return 0;
+
+ /* Use the lookup table for the good signal range. */
+ return ksz_sqi_mapping[avg_raw_sqi];
+}
+
+static int kszphy_get_sqi_max(struct phy_device *phydev)
+{
+ return KSZ9477_SQI_MAX;
+}
+
static void kszphy_enable_clk(struct phy_device *phydev)
{
struct kszphy_priv *priv = phydev->priv;
@@ -5801,6 +5923,8 @@ static struct phy_driver ksphy_driver[] = {
.update_stats = kszphy_update_stats,
.cable_test_start = ksz9x31_cable_test_start,
.cable_test_get_status = ksz9x31_cable_test_get_status,
+ .get_sqi = kszphy_get_sqi,
+ .get_sqi_max = kszphy_get_sqi_max,
} };
module_phy_driver(ksphy_driver);
--
2.39.5
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