Subject: Re: [PATCH net-next v3 2/4] net: ethernet: altera-tse: Convert to mdio-regmap and use PCS Lynx

From: "Russell King (Oracle)" <[email-masked]>
Date: Fri, 26 May 2023 10:05:17 +0100

On Fri, May 26, 2023 at 10:39:08AM +0200, Simon Horman wrote:
> On Fri, May 26, 2023 at 09:42:50AM +0200, Maxime Chevallier wrote:
> > The newly introduced regmap-based MDIO driver allows for an easy mapping
> > of an mdiodevice onto the memory-mapped TSE PCS, which is actually a
> > Lynx PCS.
> > 
> > Convert Altera TSE to use this PCS instead of the pcs-altera-tse, which
> > is nothing more than a memory-mapped Lynx PCS.
> > 
> > Signed-off-by: Maxime Chevallier <[email-masked]>
> 
> Hi Maxime,
> 
> I have some concerns about the error paths in this patch.

We've had similar problems with mdio_device_create() vs the XPCS
driver.

I think it's time that we made this easier for users.

diff --git a/drivers/net/pcs/pcs-xpcs.c b/drivers/net/pcs/pcs-xpcs.c
index b87c69c4cdd7..802222581feb 100644
--- a/drivers/net/pcs/pcs-xpcs.c
+++ b/drivers/net/pcs/pcs-xpcs.c
@@ -1240,6 +1240,7 @@ struct dw_xpcs *xpcs_create(struct mdio_device *mdiodev,
 	if (!xpcs)
 		return ERR_PTR(-ENOMEM);
 
+	mdio_device_get(mdiodev);
 	xpcs->mdiodev = mdiodev;
 
 	xpcs_id = xpcs_get_id(xpcs);
@@ -1272,6 +1273,7 @@ struct dw_xpcs *xpcs_create(struct mdio_device *mdiodev,
 	ret = -ENODEV;
 
 out:
+	mdio_device_put(mdiodev);
 	kfree(xpcs);
 
 	return ERR_PTR(ret);
@@ -1280,8 +1282,33 @@ EXPORT_SYMBOL_GPL(xpcs_create);
 
 void xpcs_destroy(struct dw_xpcs *xpcs)
 {
+	mdio_device_put(mdiodev);
 	kfree(xpcs);
 }
 EXPORT_SYMBOL_GPL(xpcs_destroy);
 
+struct dw_xpcs *xpcs_create_mdiodev(struct mii_bus *bus, int addr,
+				    phy_interface_t interface)
+{
+	struct mdio_device *mdiodev;
+	struct dw_xpcs *xpcs;
+
+	mdiodev = mdio_device_create(bus, addr);
+	if (IS_ERR(mdiodev))
+		return ERR_CAST(mdiodev);
+
+	xpcs = xpcs_create(mdiodev, interface);
+
+	/* xpcs_create() has taken a refcount on the mdiodev if it was
+	 * successful. If xpcs_create() fails, this will free the mdio
+	 * device here. In any case, we don't need to hold our reference
+	 * anymore, and putting it here will allow mdio_device_put() in
+	 * xpcs_destroy() to automatically free the mdio device.
+	 */
+	mdio_device_put(mdiodev);
+
+	return xpcs;
+}
+EXPORT_SYMBOL_GPL(xpcs_create_mdiodev);
+
 MODULE_LICENSE("GPL v2");
diff --git a/include/linux/mdio.h b/include/linux/mdio.h
index 1d7d550bbf1a..537b62330c90 100644
--- a/include/linux/mdio.h
+++ b/include/linux/mdio.h
@@ -108,6 +108,16 @@ int mdio_driver_register(struct mdio_driver *drv);
 void mdio_driver_unregister(struct mdio_driver *drv);
 int mdio_device_bus_match(struct device *dev, struct device_driver *drv);
 
+static inline void mdio_device_get(struct mdio_device *mdiodev)
+{
+	get_device(&mdiodev->dev);
+}
+
+static inline void mdio_device_put(struct mdio_device *mdiodev)
+{
+	mdio_device_free(mdiodev);
+}
+
 static inline bool mdio_phy_id_is_c45(int phy_id)
 {
 	return (phy_id & MDIO_PHY_ID_C45) && !(phy_id & ~MDIO_PHY_ID_C45_MASK);

The same for pcs-lynx. That way we remove the need for driver authors
to get the creation and destruction of the mdio device correct
without messing up the existing users - they only have to worry about
creating the PCS via the xxx_create_mdiodev() function and destroying
it via xxx_destroy().

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!