net: add helpers to resolve negotiated flow control

Add a couple of helpers to resolve negotiated flow control. Two helpers
are provided:

- linkmode_resolve_pause() which takes the link partner and local
  advertisements, and decodes whether we should enable TX or RX pause
  at the MAC. This is useful outside of phylib, e.g. in phylink.
- phy_get_pause(), which returns the TX/RX enablement status for the
  current negotiation results of the PHY.

This allows us to centralise the flow control resolution, rather than
spreading it around.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 44 insertions, 0 deletions

diff --git a/drivers/net/phy/linkmode.c b/drivers/net/phy/linkmode.c
new file mode 100644
index 000000000000..969918795228
--- /dev/null
+++ b/drivers/net/phy/linkmode.c
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0+
+#include <linux/linkmode.h>
+
+/**
+ * linkmode_resolve_pause - resolve the allowable pause modes
+ * @local_adv: local advertisement in ethtool format
+ * @partner_adv: partner advertisement in ethtool format
+ * @tx_pause: pointer to bool to indicate whether transmit pause should be
+ * enabled.
+ * @rx_pause: pointer to bool to indicate whether receive pause should be
+ * enabled.
+ *
+ * Flow control is resolved according to our and the link partners
+ * advertisements using the following drawn from the 802.3 specs:
+ *  Local device  Link partner
+ *  Pause AsymDir Pause AsymDir Result
+ *    0     X       0     X     Disabled
+ *    0     1       1     0     Disabled
+ *    0     1       1     1     TX
+ *    1     0       0     X     Disabled
+ *    1     X       1     X     TX+RX
+ *    1     1       0     1     RX
+ */
+void linkmode_resolve_pause(const unsigned long *local_adv,
+			    const unsigned long *partner_adv,
+			    bool *tx_pause, bool *rx_pause)
+{
+	__ETHTOOL_DECLARE_LINK_MODE_MASK(m);
+
+	linkmode_and(m, local_adv, partner_adv);
+	if (linkmode_test_bit(ETHTOOL_LINK_MODE_Pause_BIT, m)) {
+		*tx_pause = true;
+		*rx_pause = true;
+	} else if (linkmode_test_bit(ETHTOOL_LINK_MODE_Asym_Pause_BIT, m)) {
+		*tx_pause = linkmode_test_bit(ETHTOOL_LINK_MODE_Pause_BIT,
+					      partner_adv);
+		*rx_pause = linkmode_test_bit(ETHTOOL_LINK_MODE_Pause_BIT,
+					      local_adv);
+	} else {
+		*tx_pause = false;
+		*rx_pause = false;
+	}
+}
+EXPORT_SYMBOL_GPL(linkmode_resolve_pause);