[PATCH phy-next 1/3] phy: lynx-28g: use timeouts when waiting for lane halt and reset

[Vladimir Oltean]

There are various circumstances in which a lane halt, or a lane reset,
will fail to complete. If this happens, it will hang the kernel, which
only implements a busy loop with no timeout.

The circumstances in which this will happen are all bugs in nature:
- if we try to power off a powered off lane
- if we try to power off a lane that uses a PLL locked onto the wrong
  refclk frequency (wrong RCW, but SoC boots anyway)

Actually, unbounded loops in the kernel are a bad practice, so let's use
read_poll_timeout() with a custom function that reads both LNaTRSTCTL
(lane transmit control register) and LNaRRSTCTL (lane receive control
register) and returns true when the request is done in both directions.

The HLT_REQ bit has to clear, whereas the RST_DONE bit has to get set.

Any time such an error happens, it is catastrophic and there is no point
in trying to propagate it to our callers:
- if lynx_28g_set_mode() -> lynx_28g_power_on() times out, we have
  already reconfigured the lane, but returning an error would tell the
  caller that we didn't
- if lynx_28g_power_off() times out, again not much for the consumer to
  do to help get out of this situation - the phy_power_off() call is
  probably made from a context that the consumer can't cancel, or it is
  making it to return to a known state from a previous failure.

So just print an error if timeouts happen and let the driver control
flow continue. The entire point is just to not let the kernel freeze.

Suggested-by: Josua Mayer <josua@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/d0c8bbf8-a0c5-469f-a148-de2235948c0f@xxxxxxxxxxxxx/
Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
---
Previously submitted as part of larger set:
https://lore.kernel.org/linux-phy/20260114152111.625350-7-vladimir.oltean@xxxxxxx/

Changes:
- Stop propagating the read_poll_timeout() errors to callers
- Adjust commit message to explain that decision
---
 drivers/phy/freescale/phy-fsl-lynx-28g.c | 72 ++++++++++++++++++------
 1 file changed, 56 insertions(+), 16 deletions(-)

diff --git a/drivers/phy/freescale/phy-fsl-lynx-28g.c b/drivers/phy/freescale/phy-fsl-lynx-28g.c
index 2b0fd95ba62f..3debf4131e0f 100644
--- a/drivers/phy/freescale/phy-fsl-lynx-28g.c
+++ b/drivers/phy/freescale/phy-fsl-lynx-28g.c
@@ -249,6 +249,12 @@
 
 #define CR(x)					((x) * 4)
 
+#define LYNX_28G_LANE_HALT_SLEEP_US		100
+#define LYNX_28G_LANE_HALT_TIMEOUT_US		1000000
+
+#define LYNX_28G_LANE_RESET_SLEEP_US		100
+#define LYNX_28G_LANE_RESET_TIMEOUT_US		1000000
+
 enum lynx_28g_eq_type {
 	EQ_TYPE_NO_EQ = 0,
 	EQ_TYPE_2TAP = 1,
@@ -600,10 +606,29 @@ static void lynx_28g_lane_set_pll(struct lynx_28g_lane *lane,
 	}
 }
 
+static bool lynx_28g_lane_halt_done(struct lynx_28g_lane *lane)
+{
+	u32 trstctl = lynx_28g_lane_read(lane, LNaTRSTCTL);
+	u32 rrstctl = lynx_28g_lane_read(lane, LNaRRSTCTL);
+
+	return !(trstctl & LNaTRSTCTL_HLT_REQ) &&
+	       !(rrstctl & LNaRRSTCTL_HLT_REQ);
+}
+
+static bool lynx_28g_lane_reset_done(struct lynx_28g_lane *lane)
+{
+	u32 trstctl = lynx_28g_lane_read(lane, LNaTRSTCTL);
+	u32 rrstctl = lynx_28g_lane_read(lane, LNaRRSTCTL);
+
+	return (trstctl & LNaTRSTCTL_RST_DONE) &&
+	       (rrstctl & LNaRRSTCTL_RST_DONE);
+}
+
 static int lynx_28g_power_off(struct phy *phy)
 {
 	struct lynx_28g_lane *lane = phy_get_drvdata(phy);
-	u32 trstctl, rrstctl;
+	bool done;
+	int err;
 
 	if (!lane->powered_up)
 		return 0;
@@ -615,11 +640,14 @@ static int lynx_28g_power_off(struct phy *phy)
 			  LNaRRSTCTL_HLT_REQ);
 
 	/* Wait until the halting process is complete */
-	do {
-		trstctl = lynx_28g_lane_read(lane, LNaTRSTCTL);
-		rrstctl = lynx_28g_lane_read(lane, LNaRRSTCTL);
-	} while ((trstctl & LNaTRSTCTL_HLT_REQ) ||
-		 (rrstctl & LNaRRSTCTL_HLT_REQ));
+	err = read_poll_timeout(lynx_28g_lane_halt_done, done, done,
+				LYNX_28G_LANE_HALT_SLEEP_US,
+				LYNX_28G_LANE_HALT_TIMEOUT_US,
+				false, lane);
+	if (err) {
+		dev_err(&phy->dev, "Lane %c halt failed: %pe\n",
+			'A' + lane->id, ERR_PTR(err));
+	}
 
 	lane->powered_up = false;
 
@@ -629,7 +657,8 @@ static int lynx_28g_power_off(struct phy *phy)
 static int lynx_28g_power_on(struct phy *phy)
 {
 	struct lynx_28g_lane *lane = phy_get_drvdata(phy);
-	u32 trstctl, rrstctl;
+	bool done;
+	int err;
 
 	if (lane->powered_up)
 		return 0;
@@ -641,11 +670,14 @@ static int lynx_28g_power_on(struct phy *phy)
 			  LNaRRSTCTL_RST_REQ);
 
 	/* Wait until the reset sequence is completed */
-	do {
-		trstctl = lynx_28g_lane_read(lane, LNaTRSTCTL);
-		rrstctl = lynx_28g_lane_read(lane, LNaRRSTCTL);
-	} while (!(trstctl & LNaTRSTCTL_RST_DONE) ||
-		 !(rrstctl & LNaRRSTCTL_RST_DONE));
+	err = read_poll_timeout(lynx_28g_lane_reset_done, done, done,
+				LYNX_28G_LANE_RESET_SLEEP_US,
+				LYNX_28G_LANE_RESET_TIMEOUT_US,
+				false, lane);
+	if (err) {
+		dev_err(&phy->dev, "Lane %c reset failed: %pe\n",
+			'A' + lane->id, ERR_PTR(err));
+	}
 
 	lane->powered_up = true;
 
@@ -1065,7 +1097,7 @@ static void lynx_28g_cdr_lock_check(struct work_struct *work)
 	struct lynx_28g_priv *priv = work_to_lynx(work);
 	struct lynx_28g_lane *lane;
 	u32 rrstctl;
-	int i;
+	int err, i;
 
 	for (i = 0; i < LYNX_28G_NUM_LANE; i++) {
 		lane = &priv->lane[i];
@@ -1081,9 +1113,17 @@ static void lynx_28g_cdr_lock_check(struct work_struct *work)
 		if (!(rrstctl & LNaRRSTCTL_CDR_LOCK)) {
 			lynx_28g_lane_rmw(lane, LNaRRSTCTL, LNaRRSTCTL_RST_REQ,
 					  LNaRRSTCTL_RST_REQ);
-			do {
-				rrstctl = lynx_28g_lane_read(lane, LNaRRSTCTL);
-			} while (!(rrstctl & LNaRRSTCTL_RST_DONE));
+
+			err = read_poll_timeout(lynx_28g_lane_read, rrstctl,
+						!!(rrstctl & LNaRRSTCTL_RST_DONE),
+						LYNX_28G_LANE_RESET_SLEEP_US,
+						LYNX_28G_LANE_RESET_TIMEOUT_US,
+						false, lane, LNaRRSTCTL);
+			if (err) {
+				dev_warn_once(&lane->phy->dev,
+					      "Lane %c receiver reset failed: %pe\n",
+					      'A' + lane->id, ERR_PTR(err));
+			}
 		}
 
 		mutex_unlock(&lane->phy->mutex);
-- 
2.34.1