[PATCH v5] net: dsa: mt7530: fix impossible MDIO address and issue warning

[PATCH v5] net: dsa: mt7530: fix impossible MDIO address and issue warning

[Daniel Golle]

The MDIO address of the MT7530 and MT7531 switch ICs can be configured
using bootstrap pins. However, there are only 4 possible options for the
switch itself: 7, 15, 23 and 31. As in MediaTek's SDK the address of the
switch is wrongly stated in the device tree as 0 (while in reality it is
31), warn the user about such broken device tree and make a good guess
what was actually intended.

This is necessary to not break compatibility with existing Device Trees
wrongly declaring the switch to be present at address 0 or 1, as with
commit 868ff5f4944a ("net: dsa: mt7530-mdio: read PHY address of switch
from device tree") the address in device tree will be taken into
account, while before it was hard-coded in the driver to 0x1f
independently of the value in Device Tree.

Fixes: b8f126a8d543 ("net-next: dsa: add dsa support for Mediatek MT7530 switch")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Reviewed-by: Arınç ÜNAL <arinc.unal@arinc9.com>
---
Changes since v4 [4]:
 - fix indentation
 - bring back parentheses to satisfy GCC
 - print warning before registering new device to avoid confusing
   order of messages in kernel log
 - improve commit message

Changes since v3 [3]:
 - simplify calculation of correct address

Changes since v2 [2]:
 - use macros instead of magic numbers
 - introduce helper functions
 - register new device on MDIO bus instead of messing with the address
   and schedule delayed_work to unregister the "wrong" device.
   This is a slightly different approach than suggested by Russell, but
   imho makes things much easier than keeping the "wrong" device and
   having to deal with keeping the removal of both devices linked.
 - improve comments

Changes since v1 [1]:
 - use FW_WARN as suggested.
 - fix build on net tree which doesn't have 'mdiodev' as member of the
   priv struct. Imho including this patch as fix makes sense to warn
   users about broken firmware, even if the change introducing the
   actual breakage is only present in net-next for now.

[1]: https://patchwork.kernel.org/project/netdevbpf/patch/e615351aefba25e990215845e4812e6cb8153b28.1714433716.git.daniel@makrotopia.org/
[2]: https://patchwork.kernel.org/project/netdevbpf/patch/11f5f127d0350e72569c36f9060b6e642dfaddbb.1714514208.git.daniel@makrotopia.org/
[3]: https://patchwork.kernel.org/project/netdevbpf/patch/7e3fed489c0bbca84a386b1077c61589030ff4ab.1719963228.git.daniel@makrotopia.org/
[4]: https://patchwork.kernel.org/project/netdevbpf/patch/1c378be54d0fb76117f6d72dadd4a43a9950f0dc.1720105125.git.daniel@makrotopia.org/

 drivers/net/dsa/mt7530-mdio.c | 92 +++++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)

diff --git a/drivers/net/dsa/mt7530-mdio.c b/drivers/net/dsa/mt7530-mdio.c
index 51df42ccdbe6..c666edec6b9e 100644
--- a/drivers/net/dsa/mt7530-mdio.c
+++ b/drivers/net/dsa/mt7530-mdio.c
@@ -11,6 +11,7 @@
 #include <linux/regmap.h>
 #include <linux/reset.h>
 #include <linux/regulator/consumer.h>
+#include <linux/workqueue.h>
 #include <net/dsa.h>
 
 #include "mt7530.h"
@@ -136,6 +137,93 @@ static const struct of_device_id mt7530_of_match[] = {
 };
 MODULE_DEVICE_TABLE(of, mt7530_of_match);
 
+static int
+mt7530_correct_addr(int phy_addr)
+{
+	/* The corrected address is calculated as stated below:
+	 *  0 ~  6, 31 -> 31
+	 *  7 ~ 14     -> 7
+	 * 15 ~ 22     -> 15
+	 * 23 ~ 30     -> 23
+	 */
+	return (((phy_addr - MT7530_NUM_PORTS) & ~MT7530_NUM_PORTS) +
+		MT7530_NUM_PORTS) & (PHY_MAX_ADDR - 1);
+}
+
+static bool
+mt7530_is_invalid_addr(int phy_addr)
+{
+	/* Only MDIO bus addresses 7, 15, 23, and 31 are valid options,
+	 * which all have the least significant three bits set. Check
+	 * for this.
+	 */
+	return (phy_addr & MT7530_NUM_PORTS) != MT7530_NUM_PORTS;
+}
+
+struct remove_impossible_priv {
+	struct delayed_work remove_impossible_work;
+	struct mdio_device *mdiodev;
+};
+
+static void
+mt7530_remove_impossible(struct work_struct *work)
+{
+	struct remove_impossible_priv *priv = container_of(work, struct remove_impossible_priv,
+							   remove_impossible_work.work);
+	struct mdio_device *mdiodev = priv->mdiodev;
+
+	mdio_device_remove(mdiodev);
+	mdio_device_free(mdiodev);
+	kfree(priv);
+}
+
+static int
+mt7530_reregister(struct mdio_device *mdiodev)
+{
+	/* If the address in DT must be wrong, make a good guess about
+	 * the most likely intention, issue a warning, register a new
+	 * MDIO device at the correct address and schedule the removal
+	 * of the device having an impossible address.
+	 */
+	struct fwnode_handle *fwnode = dev_fwnode(&mdiodev->dev);
+	int corrected_addr = mt7530_correct_addr(mdiodev->addr);
+	struct remove_impossible_priv *rem_priv;
+	struct mdio_device *new_mdiodev;
+	int ret;
+
+	dev_warn(&mdiodev->dev, FW_WARN
+		 "impossible switch MDIO address in device tree, assuming %d\n",
+		 corrected_addr);
+
+	rem_priv = kmalloc(sizeof(*rem_priv), GFP_KERNEL);
+	if (!rem_priv)
+		return -ENOMEM;
+
+	new_mdiodev = mdio_device_create(mdiodev->bus, corrected_addr);
+	if (IS_ERR(new_mdiodev)) {
+		ret = PTR_ERR(new_mdiodev);
+		goto out_free_work;
+	}
+	device_set_node(&new_mdiodev->dev, fwnode);
+
+	ret = mdio_device_register(new_mdiodev);
+	if (WARN_ON(ret))
+		goto out_free_dev;
+
+	/* schedule impossible device for removal from mdio bus */
+	rem_priv->mdiodev = mdiodev;
+	INIT_DELAYED_WORK(&rem_priv->remove_impossible_work, mt7530_remove_impossible);
+	schedule_delayed_work(&rem_priv->remove_impossible_work, 0);
+
+	return -EFAULT;
+
+out_free_dev:
+	mdio_device_free(new_mdiodev);
+out_free_work:
+	kfree(rem_priv);
+	return ret;
+}
+
 static int
 mt7530_probe(struct mdio_device *mdiodev)
 {
@@ -144,6 +232,10 @@ mt7530_probe(struct mdio_device *mdiodev)
 	struct device_node *dn;
 	int ret;
 
+	/* Check and if needed correct the MDIO address of the switch */
+	if (mt7530_is_invalid_addr(mdiodev->addr))
+		return mt7530_reregister(mdiodev);
+
 	dn = mdiodev->dev.of_node;
 
 	priv = devm_kzalloc(&mdiodev->dev, sizeof(*priv), GFP_KERNEL);
-- 
2.45.2

Re: [PATCH v5] net: dsa: mt7530: fix impossible MDIO address and issue warning

[Daniel Golle]

I've just noticed that I forgot to include the target tree name in the
patch subject. Being a fix this is intended to be applied on 'net'.

Re: [PATCH v5] net: dsa: mt7530: fix impossible MDIO address and issue warning

[Vladimir Oltean]

On Fri, Jul 05, 2024 at 11:48:40AM +0100, Daniel Golle wrote:
> The MDIO address of the MT7530 and MT7531 switch ICs can be configured
> using bootstrap pins. However, there are only 4 possible options for the
> switch itself: 7, 15, 23 and 31. As in MediaTek's SDK the address of the
> switch is wrongly stated in the device tree as 0 (while in reality it is
> 31), warn the user about such broken device tree and make a good guess
> what was actually intended.
> 
> This is necessary to not break compatibility with existing Device Trees
> wrongly declaring the switch to be present at address 0 or 1, as with
> commit 868ff5f4944a ("net: dsa: mt7530-mdio: read PHY address of switch
> from device tree") the address in device tree will be taken into
> account, while before it was hard-coded in the driver to 0x1f
> independently of the value in Device Tree.
> 
> Fixes: b8f126a8d543 ("net-next: dsa: add dsa support for Mediatek MT7530 switch")
> Signed-off-by: Daniel Golle <daniel@makrotopia.org>
> Reviewed-by: Andrew Lunn <andrew@lunn.ch>
> Tested-by: Arınç ÜNAL <arinc.unal@arinc9.com>
> Reviewed-by: Arınç ÜNAL <arinc.unal@arinc9.com>
> ---

Despite having commented on v3, I am not going to leave a review tag on
this patch. Its contents has nothing to do with DSA, so I have no
technical objections of my own, plus little authority for an ack.
It basically boils down to whether the phylib maintainers are okay with
this use of mdio_device_remove() API from mdio_device drivers
themselves.

I did have a technical concern in v3 about a race between the finishing
of probe() and the call to mdio_device_remove(), which Daniel did not
respond to, but I suspect that __device_driver_lock() from
drivers/base/dd.c will serialize those.

Re: [PATCH v5] net: dsa: mt7530: fix impossible MDIO address and issue warning

[Vladimir Oltean]

On Mon, Jul 08, 2024 at 04:33:59PM +0300, Vladimir Oltean wrote:
> On Fri, Jul 05, 2024 at 11:48:40AM +0100, Daniel Golle wrote:
> > The MDIO address of the MT7530 and MT7531 switch ICs can be configured
> > using bootstrap pins. However, there are only 4 possible options for the
> > switch itself: 7, 15, 23 and 31. As in MediaTek's SDK the address of the
> > switch is wrongly stated in the device tree as 0 (while in reality it is
> > 31), warn the user about such broken device tree and make a good guess
> > what was actually intended.
> > 
> > This is necessary to not break compatibility with existing Device Trees
> > wrongly declaring the switch to be present at address 0 or 1, as with
> > commit 868ff5f4944a ("net: dsa: mt7530-mdio: read PHY address of switch
> > from device tree") the address in device tree will be taken into
> > account, while before it was hard-coded in the driver to 0x1f
> > independently of the value in Device Tree.
> > 
> > Fixes: b8f126a8d543 ("net-next: dsa: add dsa support for Mediatek MT7530 switch")
> > Signed-off-by: Daniel Golle <daniel@makrotopia.org>
> > Reviewed-by: Andrew Lunn <andrew@lunn.ch>
> > Tested-by: Arınç ÜNAL <arinc.unal@arinc9.com>
> > Reviewed-by: Arınç ÜNAL <arinc.unal@arinc9.com>
> > ---
> 
> Despite having commented on v3, I am not going to leave a review tag on
> this patch. Its contents has nothing to do with DSA, so I have no
> technical objections of my own, plus little authority for an ack.
> It basically boils down to whether the phylib maintainers are okay with
> this use of mdio_device_remove() API from mdio_device drivers
> themselves.
> 
> I did have a technical concern in v3 about a race between the finishing
> of probe() and the call to mdio_device_remove(), which Daniel did not
> respond to, but I suspect that __device_driver_lock() from
> drivers/base/dd.c will serialize those.

Having that said, I noticed that this particular patch revision is not
entirely under their attention, so this is a heads up for them.
https://lore.kernel.org/netdev/f485d1d4f7b34cc2ebf3d60030d1c67b4016af3c.1720107535.git.daniel@makrotopia.org/