From XGMAC Core 3.20 and later, each Flexible PPS has individual PPSEN bit
to select Fixed mode or Flexible mode. The PPSEN must be set, or it stays
in Fixed PPS mode by default.
XGMAC Core prior 3.20, only PPSEN0(bit 4) is writable. PPSEN{1,2,3} are
read-only reserved, and they are already in Flexible mode by default, our
new code always set PPSEN{1,2,3} do not make things worse ;-)

Fixes: 95eaf3cd0a90 ("net: stmmac: dwxgmac: Add Flexible PPS support")
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Furong Xu <0x1207@gmail.com>
---
Changes in v3:
  - Tagged Fixes: and sent through net instead of net-next, thanks Jacob Keller.

Changes in v2:
  - Add comment for XGMAC_PPSEN description among different XGMAC core versions.
  - Update commit message, thanks Serge Semin.
---
 drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h     |  2 +-
 .../net/ethernet/stmicro/stmmac/dwxgmac2_core.c    | 14 +++++++++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h
index 7a8f47e7b728..a4e8b498dea9 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h
+++ b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h
@@ -259,7 +259,7 @@
 	((val) << XGMAC_PPS_MINIDX(x))
 #define XGMAC_PPSCMD_START		0x2
 #define XGMAC_PPSCMD_STOP		0x5
-#define XGMAC_PPSEN0			BIT(4)
+#define XGMAC_PPSENx(x)			BIT(4 + (x) * 8)
 #define XGMAC_PPSx_TARGET_TIME_SEC(x)	(0x00000d80 + (x) * 0x10)
 #define XGMAC_PPSx_TARGET_TIME_NSEC(x)	(0x00000d84 + (x) * 0x10)
 #define XGMAC_TRGTBUSY0			BIT(31)
diff --git a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c
index f352be269deb..453e88b75be0 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c
@@ -1178,7 +1178,19 @@ static int dwxgmac2_flex_pps_config(void __iomem *ioaddr, int index,
 
 	val |= XGMAC_PPSCMDx(index, XGMAC_PPSCMD_START);
 	val |= XGMAC_TRGTMODSELx(index, XGMAC_PPSCMD_START);
-	val |= XGMAC_PPSEN0;
+
+	/* XGMAC Core has 4 PPS outputs at most.
+	 *
+	 * Prior XGMAC Core 3.20, Fixed mode or Flexible mode are selectable for
+	 * PPS0 only via PPSEN0. PPS{1,2,3} are in Flexible mode by default,
+	 * and can not be switched to Fixed mode, since PPSEN{1,2,3} are
+	 * read-only reserved to 0.
+	 * But we always set PPSEN{1,2,3} do not make things worse ;-)
+	 *
+	 * From XGMAC Core 3.20 and later, PPSEN{0,1,2,3} are writable and must
+	 * be set, or the PPS outputs stay in Fixed PPS mode by default.
+	 */
+	val |= XGMAC_PPSENx(index);
 
 	writel(cfg->start.tv_sec, ioaddr + XGMAC_PPSx_TARGET_TIME_SEC(index));
 
-- 
2.34.1

Hello:

This patch was applied to netdev/net.git (main)
by David S. Miller <davem@davemloft.net>:

On Tue, 31 Oct 2023 10:27:29 +0800 you wrote:
> From XGMAC Core 3.20 and later, each Flexible PPS has individual PPSEN bit
> to select Fixed mode or Flexible mode. The PPSEN must be set, or it stays
> in Fixed PPS mode by default.
> XGMAC Core prior 3.20, only PPSEN0(bit 4) is writable. PPSEN{1,2,3} are
> read-only reserved, and they are already in Flexible mode by default, our
> new code always set PPSEN{1,2,3} do not make things worse ;-)
> 
> [...]

Here is the summary with links:
  - [net,v3] net: stmmac: xgmac: Enable support for multiple Flexible PPS outputs
    https://git.kernel.org/netdev/net/c/db456d90a4c1

You are awesome, thank you!
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