Revert "net: dsa: qca8k: cache lo and hi for mdio write"

This reverts commit 2481d206.

The Documentation is very confusing about the topic.
The cache logic for hi and lo is wrong and actually miss some regs to be
actually written.

What the Documentation actually intended was that it's possible to skip
writing hi OR lo if half of the reg is not needed to be written or read.

Revert the change in favor of a better and correct implementation.
Reported-by: Ronald Wahl <ronald.wahl@raritan.com>
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Cc: stable@vger.kernel.org # v5.18+
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/qca/qca8k-8xxx.c

@@ -36,44 +36,6 @@ qca8k_split_addr(u32 regaddr, u16 *r1, u16 *r2, u16 *page)
 	*page = regaddr & 0x3ff;
 }
 
-static int
-qca8k_set_lo(struct qca8k_priv *priv, int phy_id, u32 regnum, u16 lo)
-{
-	u16 *cached_lo = &priv->mdio_cache.lo;
-	struct mii_bus *bus = priv->bus;
-	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 qca8k_priv *priv, int phy_id, u32 regnum, u16 hi)
-{
-	u16 *cached_hi = &priv->mdio_cache.hi;
-	struct mii_bus *bus = priv->bus;
-	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)
 {
@@ -97,7 +59,7 @@ qca8k_mii_read32(struct mii_bus *bus, int phy_id, u32 regnum, u32 *val)
 }
 
 static void
-qca8k_mii_write32(struct qca8k_priv *priv, int phy_id, u32 regnum, u32 val)
+qca8k_mii_write32(struct mii_bus *bus, int phy_id, u32 regnum, u32 val)
 {
 	u16 lo, hi;
 	int ret;
@@ -105,9 +67,12 @@ qca8k_mii_write32(struct qca8k_priv *priv, int phy_id, u32 regnum, u32 val)
 	lo = val & 0xffff;
 	hi = (u16)(val >> 16);
 
-	ret = qca8k_set_lo(priv, phy_id, regnum, lo);
+	ret = bus->write(bus, phy_id, regnum, lo);
 	if (ret >= 0)
-		ret = qca8k_set_hi(priv, phy_id, regnum + 1, hi);
+		ret = bus->write(bus, phy_id, regnum + 1, hi);
+	if (ret < 0)
+		dev_err_ratelimited(&bus->dev,
+				    "failed to write qca8k 32bit register\n");
 }
 
 static int
@@ -442,7 +407,7 @@ qca8k_regmap_write(void *ctx, uint32_t reg, uint32_t val)
 	if (ret < 0)
 		goto exit;
 
-	qca8k_mii_write32(priv, 0x10 | r2, r1, val);
+	qca8k_mii_write32(bus, 0x10 | r2, r1, val);
 
 exit:
 	mutex_unlock(&bus->mdio_lock);
@@ -475,7 +440,7 @@ qca8k_regmap_update_bits(void *ctx, uint32_t reg, uint32_t mask, uint32_t write_
 
 	val &= ~mask;
 	val |= write_val;
-	qca8k_mii_write32(priv, 0x10 | r2, r1, val);
+	qca8k_mii_write32(bus, 0x10 | r2, r1, val);
 
 exit:
 	mutex_unlock(&bus->mdio_lock);
@@ -750,14 +715,14 @@ qca8k_mdio_write(struct qca8k_priv *priv, int phy, int regnum, u16 data)
 	if (ret)
 		goto exit;
 
-	qca8k_mii_write32(priv, 0x10 | r2, r1, val);
+	qca8k_mii_write32(bus, 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(priv, 0x10 | r2, r1, 0);
+	qca8k_mii_write32(bus, 0x10 | r2, r1, 0);
 
 	mutex_unlock(&bus->mdio_lock);
 
@@ -787,7 +752,7 @@ qca8k_mdio_read(struct qca8k_priv *priv, int phy, int regnum)
 	if (ret)
 		goto exit;
 
-	qca8k_mii_write32(priv, 0x10 | r2, r1, val);
+	qca8k_mii_write32(bus, 0x10 | r2, r1, val);
 
 	ret = qca8k_mdio_busy_wait(bus, QCA8K_MDIO_MASTER_CTRL,
 				   QCA8K_MDIO_MASTER_BUSY);
@@ -798,7 +763,7 @@ qca8k_mdio_read(struct qca8k_priv *priv, int phy, int regnum)
 
 exit:
 	/* even if the busy_wait timeouts try to clear the MASTER_EN */
-	qca8k_mii_write32(priv, 0x10 | r2, r1, 0);
+	qca8k_mii_write32(bus, 0x10 | r2, r1, 0);
 
 	mutex_unlock(&bus->mdio_lock);
 
@@ -1968,8 +1933,6 @@ 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);

drivers/net/dsa/qca/qca8k.h

@@ -375,11 +375,6 @@ 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_pcs {