[PATCH 6.18 107/227] idpf: read lower clock bits inside the time sandwich

Greg Kroah-Hartman
2026-01-28T15:56:02Z

From: Mina Almasry <almasrymina@google.com>

[ Upstream commit bdfc7b55adcd04834ccc1b6b13e55e3fd7eaa789 ]

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@google.com
Cc: namangulati@google.com
Cc: willemb@google.com
Cc: intel-wired-lan@lists.osuosl.org
Cc: milena.olech@intel.com
Cc: jacob.e.keller@intel.com

Fixes: 5cb8805d2366 ("idpf: negotiate PTP capabilities and get PTP clock")
Suggested-by: Shachar Raindel <shacharr@google.com>
Signed-off-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Samuel Salin <Samuel.salin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 3e1052d070cfd..0a8b50350b860 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);
--
2.51.0