netdev - [PATCH net-next v2 4/8] Documentation: networking: update PHY error counter diagnostics in twisted pair guide

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Message-Id: <20241219132534.725051-5-o.rempel@pengutronix.de>
Date: Thu, 19 Dec 2024 14:25:30 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Jonathan Corbet <corbet@....net>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>,
	kernel@...gutronix.de,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	Simon Horman <horms@...nel.org>,
	Russell King <linux@...linux.org.uk>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	linux-doc@...r.kernel.org
Subject: [PATCH net-next v2 4/8] Documentation: networking: update PHY error counter diagnostics in twisted pair guide

Replace generic instructions for monitoring error counters with a
procedure using the unified PHY statistics interface (`--all-groups`).

Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
 .../twisted_pair_layer1_diagnostics.rst       | 39 +++++++++++++------
 1 file changed, 28 insertions(+), 11 deletions(-)

diff --git a/Documentation/networking/diagnostic/twisted_pair_layer1_diagnostics.rst b/Documentation/networking/diagnostic/twisted_pair_layer1_diagnostics.rst
index c9be5cc7e113..079e17effadf 100644
--- a/Documentation/networking/diagnostic/twisted_pair_layer1_diagnostics.rst
+++ b/Documentation/networking/diagnostic/twisted_pair_layer1_diagnostics.rst
@@ -713,17 +713,23 @@ driver supports reporting such events.
 
 - **Monitor Error Counters**:
 
-  - While some NIC drivers and PHYs provide error counters, there is no unified
-    set of PHY-specific counters across all hardware. Additionally, not all
-    PHYs provide useful information related to errors like CRC errors, frame
-    drops, or link flaps. Therefore, this step is dependent on the specific
-    hardware and driver support.
-
-  - **Next Steps**: Use `ethtool -S <interface>` to check if your driver
-    provides useful error counters. In some cases, counters may provide
-    information about errors like link flaps or physical layer problems (e.g.,
-    excessive CRC errors), but results can vary significantly depending on the
-    PHY.
+  - Use `ethtool -S <interface> --all-groups` to retrieve standardized interface
+    statistics if the driver supports the unified interface:
+
+  - **Command:** `ethtool -S <interface> --all-groups`
+
+  - **Example Output (if supported)**:
+
+    .. code-block:: bash
+
+      phydev-RxFrames: 100391
+      phydev-RxErrors: 0
+      phydev-TxFrames: 9
+      phydev-TxErrors: 0
+
+  - If the unified interface is not supported, use `ethtool -S <interface>` to
+    retrieve MAC and PHY counters. Note that non-standardized PHY counter names
+    vary by driver and must be interpreted accordingly:
 
   - **Command:** `ethtool -S <interface>`
 
@@ -740,6 +746,17 @@ driver supports reporting such events.
     condition) or kernel log messages (e.g., link up/down events) to further
     diagnose the issue.
 
+  - **Compare Counters**:
+
+    - Compare the egress and ingress frame counts reported by the PHY and MAC.
+
+    - A small difference may occur due to sampling rate differences between the
+      MAC and PHY drivers, or if the PHY and MAC are not always fully
+      synchronized in their UP or DOWN states.
+
+    - Significant discrepancies indicate potential issues in the data path
+      between the MAC and PHY.
+
 When All Else Fails...
 ~~~~~~~~~~~~~~~~~~~~~~
 
-- 
2.39.5