diff options
Diffstat (limited to 'drivers/net/phy/dp83tg720.c')
| -rw-r--r-- | drivers/net/phy/dp83tg720.c | 185 |
1 files changed, 126 insertions, 59 deletions
diff --git a/drivers/net/phy/dp83tg720.c b/drivers/net/phy/dp83tg720.c index 7e76323409c4..391c1d868808 100644 --- a/drivers/net/phy/dp83tg720.c +++ b/drivers/net/phy/dp83tg720.c @@ -13,21 +13,92 @@ #include "open_alliance_helpers.h" /* + * DP83TG720 PHY Limitations and Workarounds + * + * The DP83TG720 1000BASE-T1 PHY has several limitations that require + * software-side mitigations. These workarounds are implemented throughout + * this driver. This section documents the known issues and their corresponding + * mitigation strategies. + * + * 1. Unreliable Link Detection and Synchronized Reset Deadlock + * ------------------------------------------------------------ + * After a link loss or during link establishment, the DP83TG720 PHY may fail + * to detect or report link status correctly. As of June 2025, no public + * errata sheet for the DP83TG720 PHY documents this behavior. + * The "DP83TC81x, DP83TG72x Software Implementation Guide" application note + * (SNLA404, available at https://www.ti.com/lit/an/snla404/snla404.pdf) + * recommends performing a soft restart if polling for a link fails to establish + * a connection after 100ms. This procedure is adopted as the workaround for the + * observed link detection issue. + * + * However, in point-to-point setups where both link partners use the same + * driver (e.g. Linux on both sides), a synchronized reset pattern may emerge. + * This leads to a deadlock, where both PHYs reset at the same time and + * continuously miss each other during auto-negotiation. + * + * To address this, the reset procedure includes two components: + * + * - A **fixed minimum delay of 1ms** after a hardware reset. The datasheet + * "DP83TG720S-Q1 1000BASE-T1 Automotive Ethernet PHY with SGMII and RGMII" + * specifies this as the "Post reset stabilization-time prior to MDC preamble + * for register access" (T6.2), ensuring the PHY is ready for MDIO + * operations. + * + * - An **additional asymmetric delay**, empirically chosen based on + * master/slave role. This reduces the risk of synchronized resets on both + * link partners. Values are selected to avoid periodic overlap and ensure + * the link is re-established within a few cycles. + * + * The functions that implement this logic are: + * - dp83tg720_soft_reset() + * - dp83tg720_get_next_update_time() + * + * 2. Polling-Based Link Detection and IRQ Support + * ----------------------------------------------- + * Due to the PHY-specific limitation described in section 1, link-up events + * cannot be reliably detected via interrupts on the DP83TG720. Therefore, + * polling is required to detect transitions from link-down to link-up. + * + * While link-down events *can* be detected via IRQs on this PHY, this driver + * currently does **not** implement interrupt support. As a result, all link + * state changes must be detected using polling. + * + * Polling behavior: + * - When the link is up: slow polling (e.g. 1s). + * - When the link just went down: fast polling for a short time. + * - When the link stays down: fallback to slow polling. + * + * This design balances responsiveness and CPU usage. It sacrifices fast link-up + * times in cases where the link is expected to remain down for extended periods, + * assuming that such systems do not require immediate reactivity. + */ + +/* * DP83TG720S_POLL_ACTIVE_LINK - Polling interval in milliseconds when the link * is active. - * DP83TG720S_POLL_NO_LINK_MIN - Minimum polling interval in milliseconds when - * the link is down. - * DP83TG720S_POLL_NO_LINK_MAX - Maximum polling interval in milliseconds when - * the link is down. + * DP83TG720S_POLL_NO_LINK - Polling interval in milliseconds when the + * link is down. + * DP83TG720S_FAST_POLL_DURATION_MS - Timeout in milliseconds for no-link + * polling after which polling interval is + * increased. + * DP83TG720S_POLL_SLOW - Slow polling interval when there is no + * link for a prolongued period. + * DP83TG720S_RESET_DELAY_MS_MASTER - Delay after a reset before attempting + * to establish a link again for master phy. + * DP83TG720S_RESET_DELAY_MS_SLAVE - Delay after a reset before attempting + * to establish a link again for slave phy. * * These values are not documented or officially recommended by the vendor but * were determined through empirical testing. They achieve a good balance in * minimizing the number of reset retries while ensuring reliable link recovery * within a reasonable timeframe. */ -#define DP83TG720S_POLL_ACTIVE_LINK 1000 -#define DP83TG720S_POLL_NO_LINK_MIN 100 -#define DP83TG720S_POLL_NO_LINK_MAX 1000 +#define DP83TG720S_POLL_ACTIVE_LINK 421 +#define DP83TG720S_POLL_NO_LINK 149 +#define DP83TG720S_FAST_POLL_DURATION_MS 6000 +#define DP83TG720S_POLL_SLOW 1117 +#define DP83TG720S_RESET_DELAY_MS_MASTER 97 +#define DP83TG720S_RESET_DELAY_MS_SLAVE 149 #define DP83TG720S_PHY_ID 0x2000a284 @@ -124,6 +195,7 @@ struct dp83tg720_stats { struct dp83tg720_priv { struct dp83tg720_stats stats; + unsigned long last_link_down_jiffies; }; /** @@ -201,6 +273,26 @@ static int dp83tg720_update_stats(struct phy_device *phydev) return 0; } +static int dp83tg720_soft_reset(struct phy_device *phydev) +{ + int ret; + + ret = phy_write(phydev, DP83TG720S_PHY_RESET, DP83TG720S_HW_RESET); + if (ret) + return ret; + + /* Include mandatory MDC-access delay (1ms) + extra asymmetric delay to + * avoid synchronized reset deadlock. See section 1 in the top-of-file + * comment block. + */ + if (phydev->master_slave_state == MASTER_SLAVE_STATE_SLAVE) + msleep(DP83TG720S_RESET_DELAY_MS_SLAVE); + else + msleep(DP83TG720S_RESET_DELAY_MS_MASTER); + + return ret; +} + static void dp83tg720_get_link_stats(struct phy_device *phydev, struct ethtool_link_ext_stats *link_stats) { @@ -382,21 +474,11 @@ static int dp83tg720_read_status(struct phy_device *phydev) /* According to the "DP83TC81x, DP83TG72x Software * Implementation Guide", the PHY needs to be reset after a * link loss or if no link is created after at least 100ms. - * - * Currently we are polling with the PHY_STATE_TIME (1000ms) - * interval, which is still enough for not automotive use cases. */ ret = phy_init_hw(phydev); if (ret) return ret; - /* Sleep 600ms for PHY stabilization post-reset. - * Empirically chosen value (not documented). - * Helps reduce reset bounces with link partners having similar - * issues. - */ - msleep(600); - /* After HW reset we need to restore master/slave configuration. * genphy_c45_pma_baset1_read_master_slave() call will be done * by the dp83tg720_config_aneg() function. @@ -477,19 +559,11 @@ static int dp83tg720_config_init(struct phy_device *phydev) { int ret; - /* Software Restart is not enough to recover from a link failure. - * Using Hardware Reset instead. - */ - ret = phy_write(phydev, DP83TG720S_PHY_RESET, DP83TG720S_HW_RESET); + /* Reset the PHY to recover from a link failure */ + ret = dp83tg720_soft_reset(phydev); if (ret) return ret; - /* Wait until MDC can be used again. - * The wait value of one 1ms is documented in "DP83TG720S-Q1 1000BASE-T1 - * Automotive Ethernet PHY with SGMII and RGMII" datasheet. - */ - usleep_range(1000, 2000); - if (phy_interface_is_rgmii(phydev)) { ret = dp83tg720_config_rgmii_delay(phydev); if (ret) @@ -525,50 +599,42 @@ static int dp83tg720_probe(struct phy_device *phydev) } /** - * dp83tg720_get_next_update_time - Determine the next update time for PHY - * state + * dp83tg720_get_next_update_time - Return next polling interval for PHY state * @phydev: Pointer to the phy_device structure * - * This function addresses a limitation of the DP83TG720 PHY, which cannot - * reliably detect or report a stable link state. To recover from such - * scenarios, the PHY must be periodically reset when the link is down. However, - * if the link partner also runs Linux with the same driver, synchronized reset - * intervals can lead to a deadlock where the link never establishes due to - * simultaneous resets on both sides. - * - * To avoid this, the function implements randomized polling intervals when the - * link is down. It ensures that reset intervals are desynchronized by - * introducing a random delay between a configured minimum and maximum range. - * When the link is up, a fixed polling interval is used to minimize overhead. - * - * This mechanism guarantees that the link will reestablish within 10 seconds - * in the worst-case scenario. + * Implements adaptive polling interval logic depending on link state and + * downtime duration. See the "2. Polling-Based Link Detection and IRQ Support" + * section at the top of this file for details. * - * Return: Time (in jiffies) until the next update event for the PHY state - * machine. + * Return: Time (in jiffies) until the next poll */ static unsigned int dp83tg720_get_next_update_time(struct phy_device *phydev) { + struct dp83tg720_priv *priv = phydev->priv; unsigned int next_time_jiffies; if (phydev->link) { - /* When the link is up, use a fixed 1000ms interval - * (in jiffies) - */ + priv->last_link_down_jiffies = 0; + + /* When the link is up, use a slower interval (in jiffies) */ next_time_jiffies = msecs_to_jiffies(DP83TG720S_POLL_ACTIVE_LINK); } else { - unsigned int min_jiffies, max_jiffies, rand_jiffies; - - /* When the link is down, randomize interval between min/max - * (in jiffies) - */ - min_jiffies = msecs_to_jiffies(DP83TG720S_POLL_NO_LINK_MIN); - max_jiffies = msecs_to_jiffies(DP83TG720S_POLL_NO_LINK_MAX); - - rand_jiffies = min_jiffies + - get_random_u32_below(max_jiffies - min_jiffies + 1); - next_time_jiffies = rand_jiffies; + unsigned long now = jiffies; + + if (!priv->last_link_down_jiffies) + priv->last_link_down_jiffies = now; + + if (time_before(now, priv->last_link_down_jiffies + + msecs_to_jiffies(DP83TG720S_FAST_POLL_DURATION_MS))) { + /* Link recently went down: fast polling */ + next_time_jiffies = + msecs_to_jiffies(DP83TG720S_POLL_NO_LINK); + } else { + /* Link has been down for a while: slow polling */ + next_time_jiffies = + msecs_to_jiffies(DP83TG720S_POLL_SLOW); + } } /* Ensure the polling time is at least one jiffy */ @@ -582,6 +648,7 @@ static struct phy_driver dp83tg720_driver[] = { .flags = PHY_POLL_CABLE_TEST, .probe = dp83tg720_probe, + .soft_reset = dp83tg720_soft_reset, .config_aneg = dp83tg720_config_aneg, .read_status = dp83tg720_read_status, .get_features = genphy_c45_pma_read_ext_abilities, |