[RFC PATCH v7 14/16] net: dsa: qca8k: cache lo and hi for mdio write

[Ansuel Smith <ansuelsmth@gmail.com>]

From Documentation, we can cache lo and hi the same way we do with the
page. This massively reduce the mdio write as 3/4 of the time as we only
require to write the lo or hi part for a mdio write.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
---
 drivers/net/dsa/qca8k.c | 60 ++++++++++++++++++++++++++++++++---------
 drivers/net/dsa/qca8k.h |  5 ++++
 2 files changed, 53 insertions(+), 12 deletions(-)

diff --git a/drivers/net/dsa/qca8k.c b/drivers/net/dsa/qca8k.c
index c2f5414033d8..2a43fb9aeef2 100644
--- a/drivers/net/dsa/qca8k.c
+++ b/drivers/net/dsa/qca8k.c
@@ -88,6 +88,42 @@ qca8k_split_addr(u32 regaddr, u16 *r1, u16 *r2, u16 *page)
 	*page = regaddr & 0x3ff;
 }
 
+static int
+qca8k_set_lo(struct mii_bus *bus, int phy_id, u32 regnum,
+	     u16 lo, u16 *cached_lo)
+{
+	int ret;
+
+	if (lo == *cached_lo)
+		return 0;
+
+	ret = bus->write(bus, phy_id, regnum, lo);
+	if (ret < 0)
+		dev_err_ratelimited(&bus->dev,
+				    "failed to write qca8k 32bit lo register\n");
+
+	*cached_lo = lo;
+	return 0;
+}
+
+static int
+qca8k_set_hi(struct mii_bus *bus, int phy_id, u32 regnum,
+	     u16 hi, u16 *cached_hi)
+{
+	int ret;
+
+	if (hi == *cached_hi)
+		return 0;
+
+	ret = bus->write(bus, phy_id, regnum, hi);
+	if (ret < 0)
+		dev_err_ratelimited(&bus->dev,
+				    "failed to write qca8k 32bit hi register\n");
+
+	*cached_hi = hi;
+	return 0;
+}
+
 static int
 qca8k_mii_read32(struct mii_bus *bus, int phy_id, u32 regnum, u32 *val)
 {
@@ -111,7 +147,8 @@ qca8k_mii_read32(struct mii_bus *bus, int phy_id, u32 regnum, u32 *val)
 }
 
 static void
-qca8k_mii_write32(struct mii_bus *bus, int phy_id, u32 regnum, u32 val)
+qca8k_mii_write32(struct mii_bus *bus, struct qca8k_mdio_cache *cache,
+		  int phy_id, u32 regnum, u32 val)
 {
 	u16 lo, hi;
 	int ret;
@@ -119,12 +156,9 @@ qca8k_mii_write32(struct mii_bus *bus, int phy_id, u32 regnum, u32 val)
 	lo = val & 0xffff;
 	hi = (u16)(val >> 16);
 
-	ret = bus->write(bus, phy_id, regnum, lo);
+	ret = qca8k_set_lo(bus, phy_id, regnum, lo, &cache->lo);
 	if (ret >= 0)
-		ret = bus->write(bus, phy_id, regnum + 1, hi);
-	if (ret < 0)
-		dev_err_ratelimited(&bus->dev,
-				    "failed to write qca8k 32bit register\n");
+		ret = qca8k_set_hi(bus, phy_id, regnum + 1, hi, &cache->hi);
 }
 
 static int
@@ -384,7 +418,7 @@ qca8k_regmap_write(void *ctx, uint32_t reg, uint32_t val)
 	if (ret < 0)
 		goto exit;
 
-	qca8k_mii_write32(bus, 0x10 | r2, r1, val);
+	qca8k_mii_write32(bus, mdio_cache, 0x10 | r2, r1, val);
 
 exit:
 	mutex_unlock(&bus->mdio_lock);
@@ -421,7 +455,7 @@ qca8k_regmap_update_bits(void *ctx, uint32_t reg, uint32_t mask, uint32_t write_
 
 	val &= ~mask;
 	val |= write_val;
-	qca8k_mii_write32(bus, 0x10 | r2, r1, val);
+	qca8k_mii_write32(bus, mdio_cache, 0x10 | r2, r1, val);
 
 exit:
 	mutex_unlock(&bus->mdio_lock);
@@ -1072,14 +1106,14 @@ qca8k_mdio_write(struct mii_bus *bus, struct qca8k_mdio_cache *cache,
 	if (ret)
 		goto exit;
 
-	qca8k_mii_write32(bus, 0x10 | r2, r1, val);
+	qca8k_mii_write32(bus, cache, 0x10 | r2, r1, val);
 
 	ret = qca8k_mdio_busy_wait(bus, QCA8K_MDIO_MASTER_CTRL,
 				   QCA8K_MDIO_MASTER_BUSY);
 
 exit:
 	/* even if the busy_wait timeouts try to clear the MASTER_EN */
-	qca8k_mii_write32(bus, 0x10 | r2, r1, 0);
+	qca8k_mii_write32(bus, cache, 0x10 | r2, r1, 0);
 
 	mutex_unlock(&bus->mdio_lock);
 
@@ -1109,7 +1143,7 @@ qca8k_mdio_read(struct mii_bus *bus, struct qca8k_mdio_cache *cache,
 	if (ret)
 		goto exit;
 
-	qca8k_mii_write32(bus, 0x10 | r2, r1, val);
+	qca8k_mii_write32(bus, cache, 0x10 | r2, r1, val);
 
 	ret = qca8k_mdio_busy_wait(bus, QCA8K_MDIO_MASTER_CTRL,
 				   QCA8K_MDIO_MASTER_BUSY);
@@ -1120,7 +1154,7 @@ qca8k_mdio_read(struct mii_bus *bus, struct qca8k_mdio_cache *cache,
 
 exit:
 	/* even if the busy_wait timeouts try to clear the MASTER_EN */
-	qca8k_mii_write32(bus, 0x10 | r2, r1, 0);
+	qca8k_mii_write32(bus, cache, 0x10 | r2, r1, 0);
 
 	mutex_unlock(&bus->mdio_lock);
 
@@ -3007,6 +3041,8 @@ qca8k_sw_probe(struct mdio_device *mdiodev)
 	}
 
 	priv->mdio_cache.page = 0xffff;
+	priv->mdio_cache.lo = 0xffff;
+	priv->mdio_cache.hi = 0xffff;
 
 	/* Check the detected switch id */
 	ret = qca8k_read_switch_id(priv);
diff --git a/drivers/net/dsa/qca8k.h b/drivers/net/dsa/qca8k.h
index 77ffdc7b5aaa..9ecd4d221906 100644
--- a/drivers/net/dsa/qca8k.h
+++ b/drivers/net/dsa/qca8k.h
@@ -369,6 +369,11 @@ struct qca8k_mdio_cache {
  * mdio writes
  */
 	u16 page;
+/* lo and hi can also be cached and from Documentation we can skip one
+ * extra mdio write if lo or hi is didn't change.
+ */
+	u16 lo;
+	u16 hi;
 };
 
 struct qca8k_priv {
-- 
2.33.1