[PATCH net-next v2 1/4] net: phylink: add ability to block carrier up

["Russell King (Oracle)" <rmk+kernel@xxxxxxxxxxxxxxx>]

Network drivers such as stmmac need to quiesce the network device prior
to changing the DMA configuration. Currently, they do this by calling
netif_carrier_off() to stop the network stack pushing packets, but this
is incompatible with phylink.

Provide a pair of functions to allow the software link state to be
blocked and brought down if necessary, and restored afterwards.

Signed-off-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx>
---
 drivers/net/phy/phylink.c | 50 +++++++++++++++++++++++++++++++++++++++
 include/linux/phylink.h   |  3 +++
 2 files changed, 53 insertions(+)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 0faa3d97e06b..d522e12f89e8 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -26,6 +26,7 @@
 
 enum {
 	PHYLINK_DISABLE_STOPPED,
+	PHYLINK_DISABLE_CARRIER,
 	PHYLINK_DISABLE_LINK,
 	PHYLINK_DISABLE_MAC_WOL,
 
@@ -83,6 +84,7 @@ struct phylink {
 	bool mac_tx_clk_stop;
 	u32 mac_tx_lpi_timer;
 	u8 mac_rx_clk_stop_blocked;
+	u8 mac_carrier_blocked;
 
 	struct sfp_bus *sfp_bus;
 	bool sfp_may_have_phy;
@@ -2456,6 +2458,54 @@ void phylink_stop(struct phylink *pl)
 }
 EXPORT_SYMBOL_GPL(phylink_stop);
 
+/**
+ * phylink_carrier_block() - unblock carrier state
+ * @pl: a pointer to a &struct phylink returned from phylink_create()
+ *
+ * Disable the software link, which will call mac_link_down(). This is to
+ * allow network drivers to safely adjust e.g. DMA settings with the
+ * device idle. All calls to phylink_carrier_block() must be balanced by
+ * the appropriate number of calls to phylink_carrier_unblock().
+ */
+void phylink_carrier_block(struct phylink *pl)
+{
+	ASSERT_RTNL();
+
+	if (pl->mac_carrier_blocked == U8_MAX) {
+		phylink_warn(pl, "%s called too many times - ignoring\n",
+			     __func__);
+		dump_stack();
+		return;
+	}
+
+	if (pl->mac_carrier_blocked++ == 0)
+		phylink_run_resolve_and_disable(pl, PHYLINK_DISABLE_CARRIER);
+}
+EXPORT_SYMBOL_GPL(phylink_carrier_block);
+
+/**
+ * phylink_carrier_unblock() - unblock carrier state
+ * @pl: a pointer to a &struct phylink returned from phylink_create()
+ *
+ * All calls to phylink_carrier_block() must be balanced with a corresponding
+ * call to phylink_carrier_unblock() to restore the carrier state.
+ */
+void phylink_carrier_unblock(struct phylink *pl)
+{
+	ASSERT_RTNL();
+
+	if (pl->mac_carrier_blocked == 0) {
+		phylink_warn(pl, "%s called too many times - ignoring\n",
+			     __func__);
+		dump_stack();
+		return;
+	}
+
+	if (--pl->mac_carrier_blocked == 0)
+		phylink_enable_and_run_resolve(pl, PHYLINK_DISABLE_CARRIER);
+}
+EXPORT_SYMBOL_GPL(phylink_carrier_unblock);
+
 /**
  * phylink_rx_clk_stop_block() - block PHY ability to stop receive clock in LPI
  * @pl: a pointer to a &struct phylink returned from phylink_create()
diff --git a/include/linux/phylink.h b/include/linux/phylink.h
index 30659b615fca..a48032561183 100644
--- a/include/linux/phylink.h
+++ b/include/linux/phylink.h
@@ -715,6 +715,9 @@ int phylink_pcs_pre_init(struct phylink *pl, struct phylink_pcs *pcs);
 void phylink_start(struct phylink *);
 void phylink_stop(struct phylink *);
 
+void phylink_carrier_block(struct phylink *);
+void phylink_carrier_unblock(struct phylink *);
+
 void phylink_rx_clk_stop_block(struct phylink *);
 void phylink_rx_clk_stop_unblock(struct phylink *);
 
-- 
2.30.2