linux-kernel - [PATCH net v1] idpf: read lower clock bits inside the time sandwich

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Message-ID: <20251211101931.2788437-1-almasrymina@google.com>
Date: Thu, 11 Dec 2025 10:19:29 +0000
From: Mina Almasry <almasrymina@...gle.com>
To: netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Mina Almasry <almasrymina@...gle.com>, Tony Nguyen <anthony.l.nguyen@...el.com>, 
	Przemek Kitszel <przemyslaw.kitszel@...el.com>, Andrew Lunn <andrew+netdev@...n.ch>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Richard Cochran <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>
Subject: [PATCH net v1] idpf: read lower clock bits inside the time sandwich

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>
---
 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);

base-commit: 885bebac9909994050bbbeed0829c727e42bd1b7
-- 
2.52.0.223.gf5cc29aaa4-goog