1. Patchew
  2. linux
  3. View series

[PATCH net-next] net: phylink: add phylink_pcs_loopback() method for PCS loopback support

Zxyan Zhu posted 1 patch 12 hours ago 
.../stmicro/stmmac/stmmac_selftests.c         | 36 ++++++++++++++-----
drivers/net/phy/phylink.c                     | 19 ++++++++++
include/linux/phylink.h                       | 16 +++++++++
3 files changed, 63 insertions(+), 8 deletions(-)
[PATCH net-next] net: phylink: add phylink_pcs_loopback() method for PCS loopback support
Posted by Zxyan Zhu 12 hours ago 
Add a pcs_loopback callback to struct phylink_pcs_ops to allow PCS
devices to expose loopback capability. This is useful for MAC drivers
running selftests on interfaces that use in-band signalling and have
no external PHY device.

The phylink_pcs_loopback() helper calls the PCS ops callback if
available, and returns -EOPNOTSUPP for PCS devices that do not
support loopback.

In stmmac, use phylink_pcs_loopback() in stmmac_test_phy_loopback()
and stmmac_selftest_run() when no phydev is present but a PCS with
loopback support exists. This enables PHY loopback selftests on
interfaces without an external PHY.

Signed-off-by: Zxyan Zhu <zxyan0222@gmail.com>
---
 .../stmicro/stmmac/stmmac_selftests.c         | 36 ++++++++++++++-----
 drivers/net/phy/phylink.c                     | 19 ++++++++++
 include/linux/phylink.h                       | 16 +++++++++
 3 files changed, 63 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c
index 29e824bd90ca..e6ac51018a65 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c
@@ -377,20 +377,36 @@ static int stmmac_test_mac_loopback(struct stmmac_priv *priv)
 static int stmmac_test_phy_loopback(struct stmmac_priv *priv)
 {
 	struct stmmac_packet_attrs attr = { };
+	struct phylink_pcs *pcs;
 	int ret;
 
-	if (!priv->dev->phydev)
-		return -EOPNOTSUPP;
+	if (priv->dev->phydev) {
+		ret = phy_loopback(priv->dev->phydev, true, 0);
+		if (ret)
+			return ret;
 
-	ret = phy_loopback(priv->dev->phydev, true, 0);
-	if (ret)
+		attr.dst = priv->dev->dev_addr;
+		ret = __stmmac_test_loopback(priv, &attr);
+
+		phy_loopback(priv->dev->phydev, false, 0);
 		return ret;
+	}
 
-	attr.dst = priv->dev->dev_addr;
-	ret = __stmmac_test_loopback(priv, &attr);
+	/* Use PCS loopback for interfaces without an external PHY. */
+	pcs = priv->hw->phylink_pcs;
+	if (pcs) {
+		ret = phylink_pcs_loopback(pcs, true);
+		if (ret)
+			return ret;
 
-	phy_loopback(priv->dev->phydev, false, 0);
-	return ret;
+		attr.dst = priv->dev->dev_addr;
+		ret = __stmmac_test_loopback(priv, &attr);
+
+		phylink_pcs_loopback(pcs, false);
+		return ret;
+	}
+
+	return -EOPNOTSUPP;
 }
 
 static int stmmac_test_mmc(struct stmmac_priv *priv)
@@ -1986,6 +2002,8 @@ void stmmac_selftest_run(struct net_device *dev,
 			ret = -EOPNOTSUPP;
 			if (dev->phydev)
 				ret = phy_loopback(dev->phydev, true, 0);
+			else if (priv->hw->phylink_pcs)
+				ret = phylink_pcs_loopback(priv->hw->phylink_pcs, true);
 			if (!ret)
 				break;
 			fallthrough;
@@ -2019,6 +2037,8 @@ void stmmac_selftest_run(struct net_device *dev,
 			ret = -EOPNOTSUPP;
 			if (dev->phydev)
 				ret = phy_loopback(dev->phydev, false, 0);
+			else if (priv->hw->phylink_pcs)
+				ret = phylink_pcs_loopback(priv->hw->phylink_pcs, false);
 			if (!ret)
 				break;
 			fallthrough;
diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 59dfe35afa54..a7f78c82913a 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -997,6 +997,25 @@ int phylink_pcs_pre_init(struct phylink *pl, struct phylink_pcs *pcs)
 }
 EXPORT_SYMBOL_GPL(phylink_pcs_pre_init);
 
+/**
+ * phylink_pcs_loopback() - Enable or disable loopback at the PCS
+ * @pcs: a pointer to a &struct phylink_pcs.
+ * @enable: true to enable loopback, false to disable
+ *
+ * Enable or disable loopback mode at the PCS level. This is used by MAC
+ * drivers for selftest purposes when no external PHY is present.
+ *
+ * Returns 0 on success, negative error code on failure.
+ */
+int phylink_pcs_loopback(struct phylink_pcs *pcs, bool enable)
+{
+	if (pcs->ops->pcs_loopback)
+		return pcs->ops->pcs_loopback(pcs, enable);
+
+	return -EOPNOTSUPP;
+}
+EXPORT_SYMBOL_GPL(phylink_pcs_loopback);
+
 static void phylink_mac_config(struct phylink *pl,
 			       const struct phylink_link_state *state)
 {
diff --git a/include/linux/phylink.h b/include/linux/phylink.h
index 2bc0db3d52ac..66c7016d4acd 100644
--- a/include/linux/phylink.h
+++ b/include/linux/phylink.h
@@ -518,6 +518,7 @@ struct phylink_pcs {
  *		    the MAC.
  * @pcs_pre_init: configure PCS components necessary for MAC hardware
  *                initialization e.g. RX clock for stmmac.
+ * @pcs_loopback: enable/disable loopback mode at the PCS.
  */
 struct phylink_pcs_ops {
 	int (*pcs_validate)(struct phylink_pcs *pcs, unsigned long *supported,
@@ -542,6 +543,7 @@ struct phylink_pcs_ops {
 	void (*pcs_disable_eee)(struct phylink_pcs *pcs);
 	void (*pcs_enable_eee)(struct phylink_pcs *pcs);
 	int (*pcs_pre_init)(struct phylink_pcs *pcs);
+	int (*pcs_loopback)(struct phylink_pcs *pcs, bool enable);
 };
 
 #if 0 /* For kernel-doc purposes only. */
@@ -717,8 +719,22 @@ void pcs_enable_eee(struct phylink_pcs *pcs);
  */
 int pcs_pre_init(struct phylink_pcs *pcs);
 
+/**
+ * pcs_loopback() - Enable or disable loopback at the PCS
+ * @pcs: a pointer to a &struct phylink_pcs.
+ * @enable: true to enable loopback, false to disable
+ *
+ * Enable or disable loopback mode at the PCS level. This is used by MAC
+ * drivers for selftest purposes when no external PHY is present.
+ *
+ * Returns 0 on success, or a negative error code on failure.
+ */
+int pcs_loopback(struct phylink_pcs *pcs, bool enable);
+
 #endif
 
+int phylink_pcs_loopback(struct phylink_pcs *pcs, bool enable);
+
 struct phylink *phylink_create(struct phylink_config *,
 			       const struct fwnode_handle *,
 			       phy_interface_t,

base-commit: 1df10cef2d1e7f9f2fb7eddb67fc70d3abf101f9
-- 
2.34.1
Re: [PATCH net-next] net: phylink: add phylink_pcs_loopback() method for PCS loopback support
Posted by Maxime Chevallier 12 hours ago 
Hi,

+Björn

On 7/24/26 10:52, Zxyan Zhu wrote:
> Add a pcs_loopback callback to struct phylink_pcs_ops to allow PCS
> devices to expose loopback capability. This is useful for MAC drivers
> running selftests on interfaces that use in-band signalling and have
> no external PHY device.
> 
> The phylink_pcs_loopback() helper calls the PCS ops callback if
> available, and returns -EOPNOTSUPP for PCS devices that do not
> support loopback.
> 
> In stmmac, use phylink_pcs_loopback() in stmmac_test_phy_loopback()
> and stmmac_selftest_run() when no phydev is present but a PCS with
> loopback support exists. This enables PHY loopback selftests on
> interfaces without an external PHY.

There have been talks about making a userspace API for loopback :

https://lore.kernel.org/netdev/20260325145022.2607545-4-bjorn@kernel.org/

Even if your patch is a pure internal feature with no uAPI parts, I wonder
if this is the correct API to have.

Maybe the right move would be to ask phylink to configure the loopback,
and let it figure-out where to do so (in the PHY ? in the PCS ? Somewhere
else ?)

With Björn's work we may end-up with an phylink api that may look like:

phylink_set_loopback(struct phylink *pl, bool enable, enum loopback_location loc)

and for cases like this one where we don't care about where the loopback
is set, we may have an enum value 'LOOPBACK_LOC_ANY' ?

Besides that, I don't see and PCS that supports that loopback, I think
it would be nice to also have the PCS code for loopback as well...

Maxime
> 
> Signed-off-by: Zxyan Zhu <zxyan0222@gmail.com>
> ---
>  .../stmicro/stmmac/stmmac_selftests.c         | 36 ++++++++++++++-----
>  drivers/net/phy/phylink.c                     | 19 ++++++++++
>  include/linux/phylink.h                       | 16 +++++++++
>  3 files changed, 63 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c
> index 29e824bd90ca..e6ac51018a65 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c
> @@ -377,20 +377,36 @@ static int stmmac_test_mac_loopback(struct stmmac_priv *priv)
>  static int stmmac_test_phy_loopback(struct stmmac_priv *priv)
>  {
>  	struct stmmac_packet_attrs attr = { };
> +	struct phylink_pcs *pcs;
>  	int ret;
>  
> -	if (!priv->dev->phydev)
> -		return -EOPNOTSUPP;
> +	if (priv->dev->phydev) {
> +		ret = phy_loopback(priv->dev->phydev, true, 0);
> +		if (ret)
> +			return ret;
>  
> -	ret = phy_loopback(priv->dev->phydev, true, 0);
> -	if (ret)
> +		attr.dst = priv->dev->dev_addr;
> +		ret = __stmmac_test_loopback(priv, &attr);
> +
> +		phy_loopback(priv->dev->phydev, false, 0);
>  		return ret;
> +	}
>  
> -	attr.dst = priv->dev->dev_addr;
> -	ret = __stmmac_test_loopback(priv, &attr);
> +	/* Use PCS loopback for interfaces without an external PHY. */
> +	pcs = priv->hw->phylink_pcs;
> +	if (pcs) {
> +		ret = phylink_pcs_loopback(pcs, true);
> +		if (ret)
> +			return ret;
>  
> -	phy_loopback(priv->dev->phydev, false, 0);
> -	return ret;
> +		attr.dst = priv->dev->dev_addr;
> +		ret = __stmmac_test_loopback(priv, &attr);
> +
> +		phylink_pcs_loopback(pcs, false);
> +		return ret;
> +	}
> +
> +	return -EOPNOTSUPP;
>  }
>  
>  static int stmmac_test_mmc(struct stmmac_priv *priv)
> @@ -1986,6 +2002,8 @@ void stmmac_selftest_run(struct net_device *dev,
>  			ret = -EOPNOTSUPP;
>  			if (dev->phydev)
>  				ret = phy_loopback(dev->phydev, true, 0);
> +			else if (priv->hw->phylink_pcs)
> +				ret = phylink_pcs_loopback(priv->hw->phylink_pcs, true);
>  			if (!ret)
>  				break;
>  			fallthrough;
> @@ -2019,6 +2037,8 @@ void stmmac_selftest_run(struct net_device *dev,
>  			ret = -EOPNOTSUPP;
>  			if (dev->phydev)
>  				ret = phy_loopback(dev->phydev, false, 0);
> +			else if (priv->hw->phylink_pcs)
> +				ret = phylink_pcs_loopback(priv->hw->phylink_pcs, false);
>  			if (!ret)
>  				break;
>  			fallthrough;
> diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
> index 59dfe35afa54..a7f78c82913a 100644
> --- a/drivers/net/phy/phylink.c
> +++ b/drivers/net/phy/phylink.c
> @@ -997,6 +997,25 @@ int phylink_pcs_pre_init(struct phylink *pl, struct phylink_pcs *pcs)
>  }
>  EXPORT_SYMBOL_GPL(phylink_pcs_pre_init);
>  
> +/**
> + * phylink_pcs_loopback() - Enable or disable loopback at the PCS
> + * @pcs: a pointer to a &struct phylink_pcs.
> + * @enable: true to enable loopback, false to disable
> + *
> + * Enable or disable loopback mode at the PCS level. This is used by MAC
> + * drivers for selftest purposes when no external PHY is present.
> + *
> + * Returns 0 on success, negative error code on failure.
> + */
> +int phylink_pcs_loopback(struct phylink_pcs *pcs, bool enable)
> +{
> +	if (pcs->ops->pcs_loopback)
> +		return pcs->ops->pcs_loopback(pcs, enable);
> +
> +	return -EOPNOTSUPP;
> +}
> +EXPORT_SYMBOL_GPL(phylink_pcs_loopback);
> +
>  static void phylink_mac_config(struct phylink *pl,
>  			       const struct phylink_link_state *state)
>  {
> diff --git a/include/linux/phylink.h b/include/linux/phylink.h
> index 2bc0db3d52ac..66c7016d4acd 100644
> --- a/include/linux/phylink.h
> +++ b/include/linux/phylink.h
> @@ -518,6 +518,7 @@ struct phylink_pcs {
>   *		    the MAC.
>   * @pcs_pre_init: configure PCS components necessary for MAC hardware
>   *                initialization e.g. RX clock for stmmac.
> + * @pcs_loopback: enable/disable loopback mode at the PCS.
>   */
>  struct phylink_pcs_ops {
>  	int (*pcs_validate)(struct phylink_pcs *pcs, unsigned long *supported,
> @@ -542,6 +543,7 @@ struct phylink_pcs_ops {
>  	void (*pcs_disable_eee)(struct phylink_pcs *pcs);
>  	void (*pcs_enable_eee)(struct phylink_pcs *pcs);
>  	int (*pcs_pre_init)(struct phylink_pcs *pcs);
> +	int (*pcs_loopback)(struct phylink_pcs *pcs, bool enable);
>  };
>  
>  #if 0 /* For kernel-doc purposes only. */
> @@ -717,8 +719,22 @@ void pcs_enable_eee(struct phylink_pcs *pcs);
>   */
>  int pcs_pre_init(struct phylink_pcs *pcs);
>  
> +/**
> + * pcs_loopback() - Enable or disable loopback at the PCS
> + * @pcs: a pointer to a &struct phylink_pcs.
> + * @enable: true to enable loopback, false to disable
> + *
> + * Enable or disable loopback mode at the PCS level. This is used by MAC
> + * drivers for selftest purposes when no external PHY is present.
> + *
> + * Returns 0 on success, or a negative error code on failure.
> + */
> +int pcs_loopback(struct phylink_pcs *pcs, bool enable);
> +
>  #endif
>  
> +int phylink_pcs_loopback(struct phylink_pcs *pcs, bool enable);
> +
>  struct phylink *phylink_create(struct phylink_config *,
>  			       const struct fwnode_handle *,
>  			       phy_interface_t,
> 
> base-commit: 1df10cef2d1e7f9f2fb7eddb67fc70d3abf101f9
Re: [PATCH net-next] net: phylink: add phylink_pcs_loopback() method for PCS loopback support
Posted by Andrew Lunn 8 hours ago 
> Besides that, I don't see and PCS that supports that loopback, I think
> it would be nice to also have the PCS code for loopback as well...

That is pretty much required for merging. We want to see both sides of
a new API.

There has also been discussion about in which direction should it
loopback. Towards the media or towards the host. For self test you
want host side, but as an exposed feature for user space to enable,
media side could also be interesting. So you should think about what
the internal API looks like to be able to specify the loop direction.

    Andrew

Patchew 2.1-devel-ea86937

© 2016 - 2026 Red Hat, Inc.