[PATCH net-next v2 0/2] Unify C22 and C45 error handling during bus enumeration

[PATCH net-next v2 0/2] Unify C22 and C45 error handling during bus enumeration

[Andrew Lunn]

When enumerating an MDIO bus, an MDIO bus driver can return -ENODEV to
a C22 read transaction to indicate there is no device at that address
on the bus. Enumeration will then continue with the next address on
the bus.

Modify C45 enumeration so that it also accepts -ENODEV and moves to
the next address on the bus, rather than consider -ENODEV as a fatal
error.

Convert the mv88e6xxx driver to return -ENODEV rather than 0xffff on
read for families which do not support C45 bus transactions. This is
more efficient, since enumeration will scan multiple devices at one
address when 0xffff is returned, where as -EONDEV immediately jumps to
the next address on the bus.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
---
Changes in v2:
- C44 -> C45 Typo
- Only return -ENODEV for unimplemented C45 read.
- Link to v1: https://lore.kernel.org/r/20240203-unify-c22-c45-scan-error-handling-v1-0-8aa9fa3c4fca@lunn.ch

---
Andrew Lunn (2):
      net: phy: c45 scanning: Don't consider -ENODEV fatal
      net: dsa: mv88e6xxx: Return -ENODEV when C45 not supported

 drivers/net/dsa/mv88e6xxx/chip.c | 2 +-
 drivers/net/phy/phy_device.c     | 8 ++++++--
 2 files changed, 7 insertions(+), 3 deletions(-)
---
base-commit: d6aa8e0aa605a6baba08220e4a83fa2619a4c4d7
change-id: 20240203-unify-c22-c45-scan-error-handling-8012bb69bbf9

Best regards,
-- 
Andrew Lunn <andrew@lunn.ch>

[PATCH net-next v2 1/2] net: phy: c45 scanning: Don't consider -ENODEV fatal

[Andrew Lunn]

When scanning the MDIO bus for C22 devices, the driver returning
-ENODEV is not considered fatal, it just indicates the MDIO bus master
knows there is no device at that address, maybe because of hardware
limitation.

Make the C45 scan code act on -ENODEV the same way, to make C22 and
C45 more uniform.

It is expected all reads for a given address will return -ENODEV, so
within get_phy_c45_ids() only the first place a read occurs has been
changed.

Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
---
 drivers/net/phy/phy_device.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 52828d1c64f7..962ab53c23ff 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -780,7 +780,7 @@ static int get_phy_c45_devs_in_pkg(struct mii_bus *bus, int addr, int dev_addr,
  * and identifiers in @c45_ids.
  *
  * Returns zero on success, %-EIO on bus access error, or %-ENODEV if
- * the "devices in package" is invalid.
+ * the "devices in package" is invalid or no device responds.
  */
 static int get_phy_c45_ids(struct mii_bus *bus, int addr,
 			   struct phy_c45_device_ids *c45_ids)
@@ -803,7 +803,11 @@ static int get_phy_c45_ids(struct mii_bus *bus, int addr,
 			 */
 			ret = phy_c45_probe_present(bus, addr, i);
 			if (ret < 0)
-				return -EIO;
+				/* returning -ENODEV doesn't stop bus
+				 * scanning
+				 */
+				return (phy_reg == -EIO ||
+					phy_reg == -ENODEV) ? -ENODEV : -EIO;
 
 			if (!ret)
 				continue;

-- 
2.43.0

Re: [PATCH net-next v2 1/2] net: phy: c45 scanning: Don't consider -ENODEV fatal

[Charles Perry]

On Sun, Feb 04, 2024 at 05:14:14PM -0600, Andrew Lunn wrote:
> When scanning the MDIO bus for C22 devices, the driver returning
> -ENODEV is not considered fatal, it just indicates the MDIO bus master
> knows there is no device at that address, maybe because of hardware
> limitation.
> 
> Make the C45 scan code act on -ENODEV the same way, to make C22 and
> C45 more uniform.
> 
> It is expected all reads for a given address will return -ENODEV, so
> within get_phy_c45_ids() only the first place a read occurs has been
> changed.
> 
> Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
> Signed-off-by: Andrew Lunn <andrew@lunn.ch>
> ---
>  drivers/net/phy/phy_device.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 52828d1c64f7..962ab53c23ff 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -780,7 +780,7 @@ static int get_phy_c45_devs_in_pkg(struct mii_bus *bus, int addr, int dev_addr,
>   * and identifiers in @c45_ids.
>   *
>   * Returns zero on success, %-EIO on bus access error, or %-ENODEV if
> - * the "devices in package" is invalid.
> + * the "devices in package" is invalid or no device responds.
>   */
>  static int get_phy_c45_ids(struct mii_bus *bus, int addr,
>  			   struct phy_c45_device_ids *c45_ids)
> @@ -803,7 +803,11 @@ static int get_phy_c45_ids(struct mii_bus *bus, int addr,
>  			 */
>  			ret = phy_c45_probe_present(bus, addr, i);
>  			if (ret < 0)
> -				return -EIO;
> +				/* returning -ENODEV doesn't stop bus
> +				 * scanning
> +				 */
> +				return (phy_reg == -EIO ||
> +					phy_reg == -ENODEV) ? -ENODEV : -EIO;

Hello Andrew,

Did you meant "ret" instead of "phy_reg" here?

"phy_reg" doesn't make sense here because you would have already returned
in the previous iteration of the loop.

Thanks,
Charles

>  
>  			if (!ret)
>  				continue;
> 
> -- 
> 2.43.0
> 
> 

Re: [PATCH net-next v2 1/2] net: phy: c45 scanning: Don't consider -ENODEV fatal

[Andrew Lunn]

On Tue, Apr 07, 2026 at 11:15:49AM -0700, Charles Perry wrote:
> On Sun, Feb 04, 2024 at 05:14:14PM -0600, Andrew Lunn wrote:
> > When scanning the MDIO bus for C22 devices, the driver returning
> > -ENODEV is not considered fatal, it just indicates the MDIO bus master
> > knows there is no device at that address, maybe because of hardware
> > limitation.
> > 
> > Make the C45 scan code act on -ENODEV the same way, to make C22 and
> > C45 more uniform.
> > 
> > It is expected all reads for a given address will return -ENODEV, so
> > within get_phy_c45_ids() only the first place a read occurs has been
> > changed.
> > 
> > Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
> > Signed-off-by: Andrew Lunn <andrew@lunn.ch>
> > ---
> >  drivers/net/phy/phy_device.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> > index 52828d1c64f7..962ab53c23ff 100644
> > --- a/drivers/net/phy/phy_device.c
> > +++ b/drivers/net/phy/phy_device.c
> > @@ -780,7 +780,7 @@ static int get_phy_c45_devs_in_pkg(struct mii_bus *bus, int addr, int dev_addr,
> >   * and identifiers in @c45_ids.
> >   *
> >   * Returns zero on success, %-EIO on bus access error, or %-ENODEV if
> > - * the "devices in package" is invalid.
> > + * the "devices in package" is invalid or no device responds.
> >   */
> >  static int get_phy_c45_ids(struct mii_bus *bus, int addr,
> >  			   struct phy_c45_device_ids *c45_ids)
> > @@ -803,7 +803,11 @@ static int get_phy_c45_ids(struct mii_bus *bus, int addr,
> >  			 */
> >  			ret = phy_c45_probe_present(bus, addr, i);
> >  			if (ret < 0)
> > -				return -EIO;
> > +				/* returning -ENODEV doesn't stop bus
> > +				 * scanning
> > +				 */
> > +				return (phy_reg == -EIO ||
> > +					phy_reg == -ENODEV) ? -ENODEV : -EIO;
> 
> Hello Andrew,
> 
> Did you meant "ret" instead of "phy_reg" here?
> 
> "phy_reg" doesn't make sense here because you would have already returned
> in the previous iteration of the loop.

Hum, good catch. That makes no sense. Looks like i cut/pasted from the
C22 code, and did not fixup the variable name.

	Andrew

[PATCH net-next v2 2/2] net: dsa: mv88e6xxx: Return -ENODEV when C45 not supported

[Andrew Lunn]

MDIO bus drivers can return -ENODEV when they know the bus does not
have a device at the given address, e.g. because of hardware
limitation. One such limitation is that the bus does not support C45
at all. This is more efficient than returning 0xffff, since it
immediately stops the probing on the given address, where as further
reads can be made when 0xffff is returned.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 6eec2e4aa031..9caecb4dfbfa 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -3659,7 +3659,7 @@ static int mv88e6xxx_mdio_read_c45(struct mii_bus *bus, int phy, int devad,
 	int err;
 
 	if (!chip->info->ops->phy_read_c45)
-		return 0xffff;
+		return -ENODEV;
 
 	mv88e6xxx_reg_lock(chip);
 	err = chip->info->ops->phy_read_c45(chip, bus, phy, devad, reg, &val);

-- 
2.43.0

Re: [PATCH net-next v2 2/2] net: dsa: mv88e6xxx: Return -ENODEV when C45 not supported

[Florian Fainelli]

On 2/4/2024 3:14 PM, Andrew Lunn wrote:
> MDIO bus drivers can return -ENODEV when they know the bus does not
> have a device at the given address, e.g. because of hardware
> limitation. One such limitation is that the bus does not support C45
> at all. This is more efficient than returning 0xffff, since it
> immediately stops the probing on the given address, where as further
> reads can be made when 0xffff is returned.
> 
> Signed-off-by: Andrew Lunn <andrew@lunn.ch>

Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
-- 
Florian

Re: [PATCH net-next v2 0/2] Unify C22 and C45 error handling during bus enumeration

[patchwork-bot+netdevbpf]

Hello:

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

On Sun, 04 Feb 2024 17:14:13 -0600 you wrote:
> When enumerating an MDIO bus, an MDIO bus driver can return -ENODEV to
> a C22 read transaction to indicate there is no device at that address
> on the bus. Enumeration will then continue with the next address on
> the bus.
> 
> Modify C45 enumeration so that it also accepts -ENODEV and moves to
> the next address on the bus, rather than consider -ENODEV as a fatal
> error.
> 
> [...]

Here is the summary with links:
  - [net-next,v2,1/2] net: phy: c45 scanning: Don't consider -ENODEV fatal
    https://git.kernel.org/netdev/net-next/c/17b447539408
  - [net-next,v2,2/2] net: dsa: mv88e6xxx: Return -ENODEV when C45 not supported
    https://git.kernel.org/netdev/net-next/c/88b3934e3f31

You are awesome, thank you!
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