[PATCH] stmmac: export RX mitigation control to device tree

[PATCH] stmmac: export RX mitigation control to device tree

[Timofey Babitskiy]

Having Rx mitigation via HW watchdog timer on is not suitable for time 
servers distributing time via NTP and PTP protocol and relying on SW 
timestamping, because Rx mitigation adds latency on receive and hence adds 
path delay assymetry, which leads to time offset on timing clients. Turning 
Rx mitigation off via platform config is not always a good option, because 
some systems use default platform configs and only tune the device tree.

Signed-off-by: Timofey Babitskiy <timofey.babitskiy@pendulum-instruments.com>
---
 Documentation/devicetree/bindings/net/snps,dwmac.yaml | 5 +++++
 drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c | 3 +++
 2 files changed, 8 insertions(+)

diff --git a/Documentation/devicetree/bindings/net/snps,dwmac.yaml b/Documentation/devicetree/bindings/net/snps,dwmac.yaml
index 4845e29411e4..b4a8d3e92b44 100644
--- a/Documentation/devicetree/bindings/net/snps,dwmac.yaml
+++ b/Documentation/devicetree/bindings/net/snps,dwmac.yaml
@@ -258,6 +258,11 @@ properties:
       is supported. For example, this is used in case of SGMII and
       MAC2MAC connection.
 
+  snps,riwt-off:
+    $ref: /schemas/types.yaml#definitions/flag
+    description:
+      Disables RX IRQ Mitigation via HW Watchdog Timer.
+
   mdio:
     type: object
     description:
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
index bedaff0c13bd..42b2f99d8c90 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
@@ -465,6 +465,9 @@ stmmac_probe_config_dt(struct platform_device *pdev, const char **mac)
        plat->en_tx_lpi_clockgating =
                of_property_read_bool(np, "snps,en-tx-lpi-clockgating");
 
+       plat->riwt_off =
+               of_property_read_bool(np, "snps,riwt-off");
+
        /* Set the maxmtu to a default of JUMBO_LEN in case the
         * parameter is not present in the device tree.
         */

Re: [PATCH] stmmac: export RX mitigation control to device tree

[David Miller]

From: Timofey Babitskiy <timofey.babitskiy@pendulum-instruments.com>
Date: Fri, 20 Dec 2019 12:56:50 +0000

> Having Rx mitigation via HW watchdog timer on is not suitable for time 
> servers distributing time via NTP and PTP protocol and relying on SW 
> timestamping, because Rx mitigation adds latency on receive and hence adds 
> path delay assymetry, which leads to time offset on timing clients. Turning 
> Rx mitigation off via platform config is not always a good option, because 
> some systems use default platform configs and only tune the device tree.
> 
> Signed-off-by: Timofey Babitskiy <timofey.babitskiy@pendulum-instruments.com>

The device tree is not an appropriate place to control what is already settable
via ethtool.

Make the appropriate ethtool setting on your NTP servers.