[net PATCH v2 0/5] net: dsa: qca8k: multiple fix on mdio read/write

[net PATCH v2 0/5] net: dsa: qca8k: multiple fix on mdio read/write

[Christian Marangi]

Due to some problems in reading the Documentation and elaborating it
some wrong assumption were done. The error was reported and notice only
now due to how things are setup in the code flow.

First 2 patch fix mgmt eth where the lenght calculation is very
confusing and in step of word size. (the related commit description have
an extensive description about how this mess works)

Last 3 patch revert the broken mdio cache and apply a correct version
that should still save some extra mdio in phy poll secnario.

These 5 patch fix each related problem and apply what the Documentation
actually say.

Changes v2:
- Add cover letter
- Fix typo in revert patch

Christian Marangi (5):
  net: dsa: qca8k: fix wrong length value for mgmt eth packet
  net: dsa: tag_qca: fix wrong MGMT_DATA2 size
  Revert "net: dsa: qca8k: cache lo and hi for mdio write"
  net: dsa: qca8k: introduce single mii read/write lo/hi
  net: dsa: qca8k: improve mdio master read/write by using single lo/hi

 drivers/net/dsa/qca/qca8k-8xxx.c | 164 ++++++++++++++++++++-----------
 drivers/net/dsa/qca/qca8k.h      |   5 -
 include/linux/dsa/tag_qca.h      |   4 +-
 3 files changed, 109 insertions(+), 64 deletions(-)

-- 
2.37.2

[net PATCH v2 1/5] net: dsa: qca8k: fix wrong length value for mgmt eth packet

[Christian Marangi]

The assumption that Documentation was right about how this value work was
wrong. It was discovered that the length value of the mgmt header is in
step of word size.

As an example to process 4 byte of data the correct length to set is 2.
To process 8 byte 4, 12 byte 6, 16 byte 8...

Odd values will always return the next size on the ack packet.
(length of 3 (6 byte) will always return 8 bytes of data)

This means that a value of 15 (0xf) actually means reading/writing 32 bytes
of data instead of 16 bytes. This behaviour is totally absent and not
documented in the switch Documentation.

In fact from Documentation the max value that mgmt eth can process is
16 byte of data while in reality it can process 32 bytes at once.

To handle this we always round up the length after deviding it for word
size. We check if the result is odd and we round another time to align
to what the switch will provide in the ack packet.
The workaround for the length limit of 15 is still needed as the length
reg max value is 0xf(15)

Reported-by: Ronald Wahl <ronald.wahl@raritan.com>
Tested-by: Ronald Wahl <ronald.wahl@raritan.com>
Fixes: 90386223f44e ("net: dsa: qca8k: add support for larger read/write size with mgmt Ethernet")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Cc: stable@vger.kernel.org # v5.18+
---
 drivers/net/dsa/qca/qca8k-8xxx.c | 45 +++++++++++++++++++++++++-------
 1 file changed, 35 insertions(+), 10 deletions(-)

diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
index c5c3b4e92f28..46151320b2a8 100644
--- a/drivers/net/dsa/qca/qca8k-8xxx.c
+++ b/drivers/net/dsa/qca/qca8k-8xxx.c
@@ -146,7 +146,16 @@ static void qca8k_rw_reg_ack_handler(struct dsa_switch *ds, struct sk_buff *skb)
 
 	command = get_unaligned_le32(&mgmt_ethhdr->command);
 	cmd = FIELD_GET(QCA_HDR_MGMT_CMD, command);
+
 	len = FIELD_GET(QCA_HDR_MGMT_LENGTH, command);
+	/* Special case for len of 15 as this is the max value for len and needs to
+	 * be increased before converting it from word to dword.
+	 */
+	if (len == 15)
+		len++;
+
+	/* We can ignore odd value, we always round up them in the alloc function. */
+	len *= sizeof(u16);
 
 	/* Make sure the seq match the requested packet */
 	if (get_unaligned_le32(&mgmt_ethhdr->seq) == mgmt_eth_data->seq)
@@ -193,17 +202,33 @@ static struct sk_buff *qca8k_alloc_mdio_header(enum mdio_cmd cmd, u32 reg, u32 *
 	if (!skb)
 		return NULL;
 
-	/* Max value for len reg is 15 (0xf) but the switch actually return 16 byte
-	 * Actually for some reason the steps are:
-	 * 0: nothing
-	 * 1-4: first 4 byte
-	 * 5-6: first 12 byte
-	 * 7-15: all 16 byte
+	/* Hdr mgmt length value is in step of word size.
+	 * As an example to process 4 byte of data the correct length to set is 2.
+	 * To process 8 byte 4, 12 byte 6, 16 byte 8...
+	 *
+	 * Odd values will always return the next size on the ack packet.
+	 * (length of 3 (6 byte) will always return 8 bytes of data)
+	 *
+	 * This means that a value of 15 (0xf) actually means reading/writing 32 bytes
+	 * of data.
+	 *
+	 * To correctly calculate the length we devide the requested len by word and
+	 * round up.
+	 * On the ack function we can skip the odd check as we already handle the
+	 * case here.
+	 */
+	real_len = DIV_ROUND_UP(len, sizeof(u16));
+
+	/* We check if the result len is odd and we round up another time to
+	 * the next size. (length of 3 will be increased to 4 as switch will always
+	 * return 8 bytes)
 	 */
-	if (len == 16)
-		real_len = 15;
-	else
-		real_len = len;
+	if (real_len % sizeof(u16) != 0)
+		real_len++;
+
+	/* Max reg value is 0xf(15) but switch will always return the next size (32 byte) */
+	if (real_len == 16)
+		real_len--;
 
 	skb_reset_mac_header(skb);
 	skb_set_network_header(skb, skb->len);
-- 
2.37.2

[net PATCH v2 2/5] net: dsa: tag_qca: fix wrong MGMT_DATA2 size

[Christian Marangi]

It was discovered that MGMT_DATA2 can contain up to 28 bytes of data
instead of the 12 bytes written in the Documentation by accounting the
limit of 16 bytes declared in Documentation subtracting the first 4 byte
in the packet header.

Update the define with the real world value.

Tested-by: Ronald Wahl <ronald.wahl@raritan.com>
Fixes: c2ee8181fddb ("net: dsa: tag_qca: add define for handling mgmt Ethernet packet")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Cc: stable@vger.kernel.org # v5.18+
---
 include/linux/dsa/tag_qca.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/dsa/tag_qca.h b/include/linux/dsa/tag_qca.h
index b1b5720d89a5..ee657452f122 100644
--- a/include/linux/dsa/tag_qca.h
+++ b/include/linux/dsa/tag_qca.h
@@ -45,8 +45,8 @@ struct sk_buff;
 					QCA_HDR_MGMT_COMMAND_LEN + \
 					QCA_HDR_MGMT_DATA1_LEN)
 
-#define QCA_HDR_MGMT_DATA2_LEN		12 /* Other 12 byte for the mdio data */
-#define QCA_HDR_MGMT_PADDING_LEN	34 /* Padding to reach the min Ethernet packet */
+#define QCA_HDR_MGMT_DATA2_LEN		28 /* Other 28 byte for the mdio data */
+#define QCA_HDR_MGMT_PADDING_LEN	18 /* Padding to reach the min Ethernet packet */
 
 #define QCA_HDR_MGMT_PKT_LEN		(QCA_HDR_MGMT_HEADER_LEN + \
 					QCA_HDR_LEN + \
-- 
2.37.2

[net PATCH v2 3/5] Revert "net: dsa: qca8k: cache lo and hi for mdio write"

[Christian Marangi]

This reverts commit 2481d206fae7884cd07014fd1318e63af35e99eb.

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+
---
 drivers/net/dsa/qca/qca8k-8xxx.c | 61 +++++++-------------------------
 drivers/net/dsa/qca/qca8k.h      |  5 ---
 2 files changed, 12 insertions(+), 54 deletions(-)

diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
index 46151320b2a8..fbcd5c2b13ae 100644
--- a/drivers/net/dsa/qca/qca8k-8xxx.c
+++ b/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);
diff --git a/drivers/net/dsa/qca/qca8k.h b/drivers/net/dsa/qca/qca8k.h
index 0b7a5cb12321..03514f7a20be 100644
--- a/drivers/net/dsa/qca/qca8k.h
+++ b/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 {
-- 
2.37.2

[net PATCH v2 4/5] net: dsa: qca8k: introduce single mii read/write lo/hi

[Christian Marangi]

It may be useful to read/write just the lo or hi half of a reg.

This is especially useful for phy poll with the use of mdio master.
The mdio master reg is composed by the first 16 bit related to setup and
the other half with the returned data or data to write.

Refactor the mii function to permit single mii read/write of lo or hi
half of the reg.

Tested-by: Ronald Wahl <ronald.wahl@raritan.com>
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
---
 drivers/net/dsa/qca/qca8k-8xxx.c | 106 ++++++++++++++++++++++++-------
 1 file changed, 84 insertions(+), 22 deletions(-)

diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
index fbcd5c2b13ae..92c4bfef7c97 100644
--- a/drivers/net/dsa/qca/qca8k-8xxx.c
+++ b/drivers/net/dsa/qca/qca8k-8xxx.c
@@ -37,42 +37,104 @@ qca8k_split_addr(u32 regaddr, u16 *r1, u16 *r2, u16 *page)
 }
 
 static int
-qca8k_mii_read32(struct mii_bus *bus, int phy_id, u32 regnum, u32 *val)
+qca8k_mii_write_lo(struct mii_bus *bus, int phy_id, u32 regnum, u32 val)
 {
 	int ret;
+	u16 lo;
 
-	ret = bus->read(bus, phy_id, regnum);
-	if (ret >= 0) {
-		*val = ret;
-		ret = bus->read(bus, phy_id, regnum + 1);
-		*val |= ret << 16;
-	}
+	lo = val & 0xffff;
+	ret = bus->write(bus, phy_id, regnum, lo);
+	if (ret < 0)
+		dev_err_ratelimited(&bus->dev,
+				    "failed to write qca8k 32bit lo register\n");
 
-	if (ret < 0) {
+	return ret;
+}
+
+static int
+qca8k_mii_write_hi(struct mii_bus *bus, int phy_id, u32 regnum, u32 val)
+{
+	int ret;
+	u16 hi;
+
+	hi = (u16)(val >> 16);
+	ret = bus->write(bus, phy_id, regnum, hi);
+	if (ret < 0)
 		dev_err_ratelimited(&bus->dev,
-				    "failed to read qca8k 32bit register\n");
-		*val = 0;
-		return ret;
-	}
+				    "failed to write qca8k 32bit hi register\n");
+
+	return ret;
+}
+
+static int
+qca8k_mii_read_lo(struct mii_bus *bus, int phy_id, u32 regnum, u32 *val)
+{
+	int ret;
+
+	ret = bus->read(bus, phy_id, regnum);
+	if (ret < 0)
+		goto err;
 
+	*val = ret & 0xffff;
 	return 0;
+
+err:
+	dev_err_ratelimited(&bus->dev,
+			    "failed to read qca8k 32bit lo register\n");
+	*val = 0;
+
+	return ret;
 }
 
-static void
-qca8k_mii_write32(struct mii_bus *bus, int phy_id, u32 regnum, u32 val)
+static int
+qca8k_mii_read_hi(struct mii_bus *bus, int phy_id, u32 regnum, u32 *val)
 {
-	u16 lo, hi;
 	int ret;
 
-	lo = val & 0xffff;
-	hi = (u16)(val >> 16);
+	ret = bus->read(bus, phy_id, regnum);
+	if (ret < 0)
+		goto err;
 
-	ret = bus->write(bus, phy_id, regnum, lo);
-	if (ret >= 0)
-		ret = bus->write(bus, phy_id, regnum + 1, hi);
+	*val = ret << 16;
+	return 0;
+
+err:
+	dev_err_ratelimited(&bus->dev,
+			    "failed to read qca8k 32bit hi register\n");
+	*val = 0;
+
+	return ret;
+}
+
+static int
+qca8k_mii_read32(struct mii_bus *bus, int phy_id, u32 regnum, u32 *val)
+{
+	u32 hi, lo;
+	int ret;
+
+	*val = 0;
+
+	ret = qca8k_mii_read_lo(bus, phy_id, regnum, &lo);
 	if (ret < 0)
-		dev_err_ratelimited(&bus->dev,
-				    "failed to write qca8k 32bit register\n");
+		goto err;
+
+	ret = qca8k_mii_read_hi(bus, phy_id, regnum + 1, &hi);
+	if (ret < 0)
+		goto err;
+
+	*val = lo | hi;
+
+err:
+	return ret;
+}
+
+static void
+qca8k_mii_write32(struct mii_bus *bus, int phy_id, u32 regnum, u32 val)
+{
+	if (qca8k_mii_write_lo(bus, phy_id, regnum, val) < 0)
+		return;
+
+	qca8k_mii_write_hi(bus, phy_id, regnum + 1, val);
 }
 
 static int
-- 
2.37.2

[net PATCH v2 5/5] net: dsa: qca8k: improve mdio master read/write by using single lo/hi

[Christian Marangi]

Improve mdio master read/write by using singe mii read/write lo/hi.

In a read and write we need to poll the mdio master regs in a busy loop
to check for a specific bit present in the upper half of the reg. We can
ignore the other half since it won't contain useful data. This will save
an additional useless read for each read and write operation.

In a read operation the returned data is present in the mdio master reg
lower half. We can ignore the other half since it won't contain useful
data. This will save an additional useless read for each read operation.

In a read operation it's needed to just set the hi half of the mdio
master reg as the lo half will be replaced by the result. This will save
an additional useless write for each read operation.

Tested-by: Ronald Wahl <ronald.wahl@raritan.com>
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
---
 drivers/net/dsa/qca/qca8k-8xxx.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
index 92c4bfef7c97..2f224b166bbb 100644
--- a/drivers/net/dsa/qca/qca8k-8xxx.c
+++ b/drivers/net/dsa/qca/qca8k-8xxx.c
@@ -740,9 +740,9 @@ qca8k_mdio_busy_wait(struct mii_bus *bus, u32 reg, u32 mask)
 
 	qca8k_split_addr(reg, &r1, &r2, &page);
 
-	ret = read_poll_timeout(qca8k_mii_read32, ret1, !(val & mask), 0,
+	ret = read_poll_timeout(qca8k_mii_read_hi, ret1, !(val & mask), 0,
 				QCA8K_BUSY_WAIT_TIMEOUT * USEC_PER_MSEC, false,
-				bus, 0x10 | r2, r1, &val);
+				bus, 0x10 | r2, r1 + 1, &val);
 
 	/* Check if qca8k_read has failed for a different reason
 	 * before returnting -ETIMEDOUT
@@ -784,7 +784,7 @@ qca8k_mdio_write(struct qca8k_priv *priv, int phy, int regnum, u16 data)
 
 exit:
 	/* even if the busy_wait timeouts try to clear the MASTER_EN */
-	qca8k_mii_write32(bus, 0x10 | r2, r1, 0);
+	qca8k_mii_write_hi(bus, 0x10 | r2, r1 + 1, 0);
 
 	mutex_unlock(&bus->mdio_lock);
 
@@ -814,18 +814,18 @@ qca8k_mdio_read(struct qca8k_priv *priv, int phy, int regnum)
 	if (ret)
 		goto exit;
 
-	qca8k_mii_write32(bus, 0x10 | r2, r1, val);
+	qca8k_mii_write_hi(bus, 0x10 | r2, r1 + 1, val);
 
 	ret = qca8k_mdio_busy_wait(bus, QCA8K_MDIO_MASTER_CTRL,
 				   QCA8K_MDIO_MASTER_BUSY);
 	if (ret)
 		goto exit;
 
-	ret = qca8k_mii_read32(bus, 0x10 | r2, r1, &val);
+	ret = qca8k_mii_read_lo(bus, 0x10 | r2, r1, &val);
 
 exit:
 	/* even if the busy_wait timeouts try to clear the MASTER_EN */
-	qca8k_mii_write32(bus, 0x10 | r2, r1, 0);
+	qca8k_mii_write_hi(bus, 0x10 | r2, r1 + 1, 0);
 
 	mutex_unlock(&bus->mdio_lock);
 
-- 
2.37.2

Re: [net PATCH v2 0/5] net: dsa: qca8k: multiple fix on mdio read/write

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (master)
by David S. Miller <davem@davemloft.net>:

On Thu, 29 Dec 2022 17:33:31 +0100 you wrote:
> Due to some problems in reading the Documentation and elaborating it
> some wrong assumption were done. The error was reported and notice only
> now due to how things are setup in the code flow.
> 
> First 2 patch fix mgmt eth where the lenght calculation is very
> confusing and in step of word size. (the related commit description have
> an extensive description about how this mess works)
> 
> [...]

Here is the summary with links:
  - [net,v2,1/5] net: dsa: qca8k: fix wrong length value for mgmt eth packet
    https://git.kernel.org/netdev/net/c/9807ae697461
  - [net,v2,2/5] net: dsa: tag_qca: fix wrong MGMT_DATA2 size
    https://git.kernel.org/netdev/net/c/d9dba91be71f
  - [net,v2,3/5] Revert "net: dsa: qca8k: cache lo and hi for mdio write"
    https://git.kernel.org/netdev/net/c/03cb9e6d0b32
  - [net,v2,4/5] net: dsa: qca8k: introduce single mii read/write lo/hi
    https://git.kernel.org/netdev/net/c/cfbd6de588ef
  - [net,v2,5/5] net: dsa: qca8k: improve mdio master read/write by using single lo/hi
    https://git.kernel.org/netdev/net/c/a4165830ca23

You are awesome, thank you!
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