netdev - [PATCH net-next] ptp: ocp: Improve PCIe delay estimation

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Message-ID: <20240904132842.559217-1-vadim.fedorenko@linux.dev>
Date: Wed,  4 Sep 2024 13:28:42 +0000
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Jakub Kicinski <kuba@...nel.org>,
	Jonathan Lemon <jonathan.lemon@...il.com>,
	Paolo Abeni <pabeni@...hat.com>,
	David Ahern <dsahern@...nel.org>
Cc: Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
	netdev@...r.kernel.org
Subject: [PATCH net-next] ptp: ocp: Improve PCIe delay estimation

The PCIe bus can be pretty busy during boot and probe function can
see excessive delays. Let's find the minimal value out of several
tests and use it as estimated value.

Signed-off-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
---
 drivers/ptp/ptp_ocp.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/drivers/ptp/ptp_ocp.c b/drivers/ptp/ptp_ocp.c
index e7479b9b90cb..22b22e605781 100644
--- a/drivers/ptp/ptp_ocp.c
+++ b/drivers/ptp/ptp_ocp.c
@@ -1561,19 +1561,22 @@ ptp_ocp_estimate_pci_timing(struct ptp_ocp *bp)
 	ktime_t start, end;
 	ktime_t delay;
 	u32 ctrl;
+	int i;
 
-	ctrl = ioread32(&bp->reg->ctrl);
-	ctrl = OCP_CTRL_READ_TIME_REQ | OCP_CTRL_ENABLE;
+	for (i = 0; i < 3; i++) {
+		ctrl = ioread32(&bp->reg->ctrl);
+		ctrl = OCP_CTRL_READ_TIME_REQ | OCP_CTRL_ENABLE;
 
-	iowrite32(ctrl, &bp->reg->ctrl);
+		iowrite32(ctrl, &bp->reg->ctrl);
 
-	start = ktime_get_ns();
+		start = ktime_get_ns();
 
-	ctrl = ioread32(&bp->reg->ctrl);
+		ctrl = ioread32(&bp->reg->ctrl);
 
-	end = ktime_get_ns();
+		end = ktime_get_ns();
 
-	delay = end - start;
+		delay = min(delay, end - start);
+	}
 	bp->ts_window_adjust = (delay >> 5) * 3;
 }
 
-- 
2.43.0