[PATCH] net: dsa: qca8k: Disable mgmt Ethernet for qca8327

[PATCH] net: dsa: qca8k: Disable mgmt Ethernet for qca8327

[Michał Kępień]

While the qca8327 switch appears to support in-band mgmt Ethernet,
prolonged use of that protocol (e.g. for polling link state) makes the
device unstable: within minutes, ports randomly go down and no traffic
is forwarded anymore.  The same issues do not occur when MDIO is used
exclusively, so ensure mgmt Ethernet is not used on the qca8327.

Signed-off-by: Michał Kępień <kernel@kempniu.pl>
---
I came across this while migrating an AR9344-based router with a QCA8327
rev. 4 switch to a DSA-aware driver.  This glitch is a pain in the neck
to troubleshoot any further as it occurs randomly, anywhere between a
minute to an hour after the switch is set up; traffic load exerted on
the switch does not seem to matter as the problem can be triggered on a
virtually idle device.  Previously working links are reported as going
down (one by one, not all at once), even though port LEDs still blink;
no traffic is forwarded; reloading qca8k does not alleviate the problem,
only power cycling seems to help.  Nothing like this happens when only
MDIO is used.  However, qca8k currently only uses MDIO as a fallback.  I
figured that simpler is better and that mgmt Ethernet should simply be
disabled for the qca8327, but I would be happy to work on some
configurable solution if that would be preferable.

 drivers/net/dsa/qca/qca8k-8xxx.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
index 4c928983b8623..1d90a23aba6bb 100644
--- a/drivers/net/dsa/qca/qca8k-8xxx.c
+++ b/drivers/net/dsa/qca/qca8k-8xxx.c
@@ -160,6 +160,11 @@ qca8k_set_page(struct qca8k_priv *priv, u16 page)
 	return 0;
 }
 
+static bool qca8k_mgmt_eth_disabled(const struct qca8k_priv *priv)
+{
+	return priv->switch_id == QCA8K_ID_QCA8327;
+}
+
 static void qca8k_rw_reg_ack_handler(struct dsa_switch *ds, struct sk_buff *skb)
 {
 	struct qca8k_mgmt_eth_data *mgmt_eth_data;
@@ -316,6 +321,9 @@ static int qca8k_read_eth(struct qca8k_priv *priv, u32 reg, u32 *val, int len)
 	bool ack;
 	int ret;
 
+	if (qca8k_mgmt_eth_disabled(priv))
+		return -ENXIO;
+
 	skb = qca8k_alloc_mdio_header(MDIO_READ, reg, NULL,
 				      QCA8K_ETHERNET_MDIO_PRIORITY, len);
 	if (!skb)
@@ -368,6 +376,9 @@ static int qca8k_write_eth(struct qca8k_priv *priv, u32 reg, u32 *val, int len)
 	bool ack;
 	int ret;
 
+	if (qca8k_mgmt_eth_disabled(priv))
+		return -ENXIO;
+
 	skb = qca8k_alloc_mdio_header(MDIO_WRITE, reg, val,
 				      QCA8K_ETHERNET_MDIO_PRIORITY, len);
 	if (!skb)
@@ -630,6 +641,9 @@ qca8k_phy_eth_command(struct qca8k_priv *priv, bool read, int phy,
 	int ret, ret1;
 	bool ack;
 
+	if (qca8k_mgmt_eth_disabled(priv))
+		return -ENXIO;
+
 	if (regnum >= QCA8K_MDIO_MASTER_MAX_REG)
 		return -EINVAL;
 
-- 
2.55.0

Re: [PATCH] net: dsa: qca8k: Disable mgmt Ethernet for qca8327

[Andrew Lunn]

On Mon, Aug 10, 2026 at 08:15:53AM +0200, Michał Kępień wrote:
> While the qca8327 switch appears to support in-band mgmt Ethernet,
> prolonged use of that protocol (e.g. for polling link state) makes the
> device unstable: within minutes, ports randomly go down and no traffic
> is forwarded anymore.  The same issues do not occur when MDIO is used
> exclusively, so ensure mgmt Ethernet is not used on the qca8327.

Do you have time to narrow down the cause?

I _think_ in band management is used for a few different
things. e.g. statistics, as you said, PHY polling etc. Rather than
turning everything off, could you try just doing PHY polling via MDIO,
but statistics via ethernet, and do an ethtool -S every so often to
see if you can trigger the problem.

Could you also check if the management packets are getting lost? Look
at the results from wait_for_completion_timeout(), is it timing out?
If so, is the retry mechanism working? When i added the Marvell
equivalent for in-band signalling i got the retry mechanism wrong, but
never noticed because i was not loosing packets.

Thanks
	Andrew

Re: [PATCH] net: dsa: qca8k: Disable mgmt Ethernet for qca8327

[Michał Kępień]

Andrew,

First of all, after taking a closer look at this issue and the driver
code, I realized that the approach I went with in the patch stemmed from
my ignorance and that I submitted it too quickly - apologies about that.

> > While the qca8327 switch appears to support in-band mgmt Ethernet,
> > prolonged use of that protocol (e.g. for polling link state) makes the
> > device unstable: within minutes, ports randomly go down and no traffic
> > is forwarded anymore.  The same issues do not occur when MDIO is used
> > exclusively, so ensure mgmt Ethernet is not used on the qca8327.
> 
> Do you have time to narrow down the cause?

Sure, I should be able to spare a few cycles on this in the upcoming
weeks.

> I _think_ in band management is used for a few different
> things. e.g. statistics, as you said, PHY polling etc. Rather than
> turning everything off, could you try just doing PHY polling via MDIO,
> but statistics via ethernet, and do an ethtool -S every so often to
> see if you can trigger the problem.

Ack, I'll try that.

> Could you also check if the management packets are getting lost? Look
> at the results from wait_for_completion_timeout(), is it timing out?

Ack.

> If so, is the retry mechanism working? When i added the Marvell
> equivalent for in-band signalling i got the retry mechanism wrong, but
> never noticed because i was not loosing packets.

Could you please point me at the exact retry mechanism you had in mind,
either the qca8k one or the Marvell equivalent?  I cannot see any in
drivers/net/dsa/qca/qca8k-8xxx.c.  If I'm reading qca8k code correctly,
when wait_for_completion_timeout() fails, its return value is just
bubbled up the call chain.

Thanks,

-- 
Best regards,
Michał Kępień

Re: [PATCH] net: dsa: qca8k: Disable mgmt Ethernet for qca8327

[Andrew Lunn]

> Could you please point me at the exact retry mechanism you had in mind,
> either the qca8k one or the Marvell equivalent?  I cannot see any in
> drivers/net/dsa/qca/qca8k-8xxx.c.  If I'm reading qca8k code correctly,
> when wait_for_completion_timeout() fails, its return value is just
> bubbled up the call chain.

With the mv88e6xxx code, if ethernet times out, i repeated the request
using MDIO. The code is not in mainline but a few users are using it.

At minimum, i would put a printk() there, and see if it happens.  It
could be unrelated to your problem...

      Andrew

Re: [PATCH] net: dsa: qca8k: Disable mgmt Ethernet for qca8327

[Christian Marangi]

On Mon, Aug 10, 2026 at 08:15:53AM +0200, Michał Kępień wrote:
> While the qca8327 switch appears to support in-band mgmt Ethernet,
> prolonged use of that protocol (e.g. for polling link state) makes the
> device unstable: within minutes, ports randomly go down and no traffic
> is forwarded anymore.  The same issues do not occur when MDIO is used
> exclusively, so ensure mgmt Ethernet is not used on the qca8327.
> 
> Signed-off-by: Michał Kępień <kernel@kempniu.pl>
> ---
> I came across this while migrating an AR9344-based router with a QCA8327
> rev. 4 switch to a DSA-aware driver.  This glitch is a pain in the neck
> to troubleshoot any further as it occurs randomly, anywhere between a
> minute to an hour after the switch is set up; traffic load exerted on
> the switch does not seem to matter as the problem can be triggered on a
> virtually idle device.  Previously working links are reported as going
> down (one by one, not all at once), even though port LEDs still blink;
> no traffic is forwarded; reloading qca8k does not alleviate the problem,
> only power cycling seems to help.  Nothing like this happens when only
> MDIO is used.  However, qca8k currently only uses MDIO as a fallback.  I
> figured that simpler is better and that mgmt Ethernet should simply be
> disabled for the qca8327, but I would be happy to work on some
> configurable solution if that would be preferable.
>

This is a long standing issue and it seems to me disabling mgmt is just a
big workaround to a real problem.

Long time ago it was reported that there seems to be a problem with the
mdio master register for external and internall access and how mgmt was
actually sending mdio command... just done by the switch. Could the 2 issue
related?

One idea might be to verify that stuff gets actually written... as Andrew
said to verify if some packets doesn't get lost or just ignored.

Also as Andrew said I would still save this for the MIB part as the 2 thing
should be unrelated.
 
>  drivers/net/dsa/qca/qca8k-8xxx.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
> index 4c928983b8623..1d90a23aba6bb 100644
> --- a/drivers/net/dsa/qca/qca8k-8xxx.c
> +++ b/drivers/net/dsa/qca/qca8k-8xxx.c
> @@ -160,6 +160,11 @@ qca8k_set_page(struct qca8k_priv *priv, u16 page)
>  	return 0;
>  }
>  
> +static bool qca8k_mgmt_eth_disabled(const struct qca8k_priv *priv)
> +{
> +	return priv->switch_id == QCA8K_ID_QCA8327;
> +}
> +

Instead of this and return ENXIO I would just not install the relevant OPs
for the tagger and use the mdio path directly...

Makes the code cleaner and less CPU cycle (the target is ath79 and powerpc
stuff)

But as said above disabling the feature is the last solution after all the
verification are done.

>  static void qca8k_rw_reg_ack_handler(struct dsa_switch *ds, struct sk_buff *skb)
>  {
>  	struct qca8k_mgmt_eth_data *mgmt_eth_data;
> @@ -316,6 +321,9 @@ static int qca8k_read_eth(struct qca8k_priv *priv, u32 reg, u32 *val, int len)
>  	bool ack;
>  	int ret;
>  
> +	if (qca8k_mgmt_eth_disabled(priv))
> +		return -ENXIO;
> +
>  	skb = qca8k_alloc_mdio_header(MDIO_READ, reg, NULL,
>  				      QCA8K_ETHERNET_MDIO_PRIORITY, len);
>  	if (!skb)
> @@ -368,6 +376,9 @@ static int qca8k_write_eth(struct qca8k_priv *priv, u32 reg, u32 *val, int len)
>  	bool ack;
>  	int ret;
>  
> +	if (qca8k_mgmt_eth_disabled(priv))
> +		return -ENXIO;
> +
>  	skb = qca8k_alloc_mdio_header(MDIO_WRITE, reg, val,
>  				      QCA8K_ETHERNET_MDIO_PRIORITY, len);
>  	if (!skb)
> @@ -630,6 +641,9 @@ qca8k_phy_eth_command(struct qca8k_priv *priv, bool read, int phy,
>  	int ret, ret1;
>  	bool ack;
>  
> +	if (qca8k_mgmt_eth_disabled(priv))
> +		return -ENXIO;
> +
>  	if (regnum >= QCA8K_MDIO_MASTER_MAX_REG)
>  		return -EINVAL;
>  
> -- 
> 2.55.0
> 

-- 
	Ansuel

Re: [PATCH] net: dsa: qca8k: Disable mgmt Ethernet for qca8327

[Michał Kępień]

> > I came across this while migrating an AR9344-based router with a QCA8327
> > rev. 4 switch to a DSA-aware driver.  This glitch is a pain in the neck
> > to troubleshoot any further as it occurs randomly, anywhere between a
> > minute to an hour after the switch is set up; traffic load exerted on
> > the switch does not seem to matter as the problem can be triggered on a
> > virtually idle device.  Previously working links are reported as going
> > down (one by one, not all at once), even though port LEDs still blink;
> > no traffic is forwarded; reloading qca8k does not alleviate the problem,
> > only power cycling seems to help.  Nothing like this happens when only
> > MDIO is used.  However, qca8k currently only uses MDIO as a fallback.  I
> > figured that simpler is better and that mgmt Ethernet should simply be
> > disabled for the qca8327, but I would be happy to work on some
> > configurable solution if that would be preferable.
> >
> 
> This is a long standing issue and it seems to me disabling mgmt is just a
> big workaround to a real problem.

Understood.  Is it a long-standing issue for the QCA mgmt Ethernet code
in general or for a specific subset of switches (or devices)?

> Long time ago it was reported that there seems to be a problem with the
> mdio master register for external and internall access and how mgmt was
> actually sending mdio command... just done by the switch. Could the 2 issue
> related?

This thread?

https://lore.kernel.org/netdev/20250425151309.30493-1-kabel@kernel.org/

If so, that was for QCA8337, on a board where the external MDIO bus has
an extra PHY attached, so it did not look like a match for my case.  Of
course, it _might_ be related to the issue I'm running into, it just did
not seem to be at first glance.

> One idea might be to verify that stuff gets actually written... as Andrew
> said to verify if some packets doesn't get lost or just ignored.

Ack.

> Also as Andrew said I would still save this for the MIB part as the 2 thing
> should be unrelated.

Got it, I'll play around with it and see what I can find out, thanks.

-- 
Best regards,
Michał Kępień

Re: [PATCH] net: dsa: qca8k: Disable mgmt Ethernet for qca8327

[Christian Marangi]

On Wed, Aug 12, 2026 at 11:14:28AM +0200, Michał Kępień wrote:
> > > I came across this while migrating an AR9344-based router with a QCA8327
> > > rev. 4 switch to a DSA-aware driver.  This glitch is a pain in the neck
> > > to troubleshoot any further as it occurs randomly, anywhere between a
> > > minute to an hour after the switch is set up; traffic load exerted on
> > > the switch does not seem to matter as the problem can be triggered on a
> > > virtually idle device.  Previously working links are reported as going
> > > down (one by one, not all at once), even though port LEDs still blink;
> > > no traffic is forwarded; reloading qca8k does not alleviate the problem,
> > > only power cycling seems to help.  Nothing like this happens when only
> > > MDIO is used.  However, qca8k currently only uses MDIO as a fallback.  I
> > > figured that simpler is better and that mgmt Ethernet should simply be
> > > disabled for the qca8327, but I would be happy to work on some
> > > configurable solution if that would be preferable.
> > >
> > 
> > This is a long standing issue and it seems to me disabling mgmt is just a
> > big workaround to a real problem.
> 
> Understood.  Is it a long-standing issue for the QCA mgmt Ethernet code
> in general or for a specific subset of switches (or devices)?
>

specific subset of switches. On ipq806x the 8337 is mounted and mgmt works
correctly without issue.

One thing I notice on a different vendor (Airoha) is that sometimes using
these indirect way to access the Switch register might introduce
interesting HW bug.

One bug that was there was that when PBUS was used to access single port
PHY register (instead of direct MDIO) the link up/down was broken. My
theory was that the Switch chip had some latch logic that was only
triggered with MDIO. Using PBUS didn't trigger such thing.

Could be that the QCA 8327 switch also have some kind of HW bug where specific
register needs to go with MDIO or some refresh/latch logic are not
correctly triggered.

An idea might be to limit the mgmt to vlan and fdb and see if the problem
is still there. (after all those are the path where mgmt would benefit due
to the multiple register access required)
 
> > Long time ago it was reported that there seems to be a problem with the
> > mdio master register for external and internall access and how mgmt was
> > actually sending mdio command... just done by the switch. Could the 2 issue
> > related?
> 
> This thread?
> 
> https://lore.kernel.org/netdev/20250425151309.30493-1-kabel@kernel.org/
> 
> If so, that was for QCA8337, on a board where the external MDIO bus has
> an extra PHY attached, so it did not look like a match for my case.  Of
> course, it _might_ be related to the issue I'm running into, it just did
> not seem to be at first glance.
> 
> > One idea might be to verify that stuff gets actually written... as Andrew
> > said to verify if some packets doesn't get lost or just ignored.
> 
> Ack.
> 
> > Also as Andrew said I would still save this for the MIB part as the 2 thing
> > should be unrelated.
> 
> Got it, I'll play around with it and see what I can find out, thanks.
> 
> -- 
> Best regards,
> Michał Kępień

-- 
	Ansuel