netdev - [PATCH net 4/4] idpf: read lower clock bits inside the time sandwich

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Message-ID: <20260120224430.410377-5-anthony.l.nguyen@intel.com>
Date: Tue, 20 Jan 2026 14:44:28 -0800
From: Tony Nguyen <anthony.l.nguyen@...el.com>
To: davem@...emloft.net,
	kuba@...nel.org,
	pabeni@...hat.com,
	edumazet@...gle.com,
	andrew+netdev@...n.ch,
	netdev@...r.kernel.org
Cc: Mina Almasry <almasrymina@...gle.com>,
	anthony.l.nguyen@...el.com,
	richardcochran@...il.com,
	lrizzo@...gle.com,
	namangulati@...gle.com,
	willemb@...gle.com,
	intel-wired-lan@...ts.osuosl.org,
	milena.olech@...el.com,
	jacob.e.keller@...el.com,
	Shachar Raindel <shacharr@...gle.com>,
	Aleksandr Loktionov <aleksandr.loktionov@...el.com>,
	Samuel Salin <Samuel.salin@...el.com>
Subject: [PATCH net 4/4] idpf: read lower clock bits inside the time sandwich

From: Mina Almasry <almasrymina@...gle.com>

PCIe reads need to be done inside the time sandwich because PCIe
writes may get buffered in the PCIe fabric and posted to the device
after the _postts completes. Doing the PCIe read inside the time
sandwich guarantees that the write gets flushed before the _postts
timestamp is taken.

Cc: lrizzo@...gle.com
Cc: namangulati@...gle.com
Cc: willemb@...gle.com
Cc: intel-wired-lan@...ts.osuosl.org
Cc: milena.olech@...el.com
Cc: jacob.e.keller@...el.com

Fixes: 5cb8805d2366 ("idpf: negotiate PTP capabilities and get PTP clock")
Suggested-by: Shachar Raindel <shacharr@...gle.com>
Signed-off-by: Mina Almasry <almasrymina@...gle.com>
Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@...el.com>
Tested-by: Samuel Salin <Samuel.salin@...el.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@...el.com>
---
 drivers/net/ethernet/intel/idpf/idpf_ptp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/idpf/idpf_ptp.c b/drivers/net/ethernet/intel/idpf/idpf_ptp.c
index 3e1052d070cf..0a8b50350b86 100644
--- a/drivers/net/ethernet/intel/idpf/idpf_ptp.c
+++ b/drivers/net/ethernet/intel/idpf/idpf_ptp.c
@@ -108,11 +108,11 @@ static u64 idpf_ptp_read_src_clk_reg_direct(struct idpf_adapter *adapter,
 	ptp_read_system_prets(sts);
 
 	idpf_ptp_enable_shtime(adapter);
+	lo = readl(ptp->dev_clk_regs.dev_clk_ns_l);
 
 	/* Read the system timestamp post PHC read */
 	ptp_read_system_postts(sts);
 
-	lo = readl(ptp->dev_clk_regs.dev_clk_ns_l);
 	hi = readl(ptp->dev_clk_regs.dev_clk_ns_h);
 
 	spin_unlock(&ptp->read_dev_clk_lock);
-- 
2.47.1