[PATCH net] net: dsa: microchip: fix KSZ8765 fiber detection

[PATCH net] net: dsa: microchip: fix KSZ8765 fiber detection

[Sebastien Royen]

The KSZ8765 is similar to the KSZ8795 but has two fiber ports.

KSZ8_PORT_STATUS_0 is used to detect fiber mode. It is currently
defined as 0x08, which is the Global Control 6 MIB Control register
and has bit 7 defined as Flush Counter.

Set KSZ8_PORT_STATUS_0 to 0x18, which is the Port 1 Status 0 register
where bit 7 is the Fiber Mode bit.

Signed-off-by: Sebastien Royen <sebastien.royen@armadeus.com>
---
 drivers/net/dsa/microchip/ksz_common.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/dsa/microchip/ksz_common.h b/drivers/net/dsa/microchip/ksz_common.h
index cbe98494578c..f6104f714a8d 100644
--- a/drivers/net/dsa/microchip/ksz_common.h
+++ b/drivers/net/dsa/microchip/ksz_common.h
@@ -853,7 +853,7 @@ static inline bool ksz_is_sgmii_port(struct ksz_device *dev, int port)
 #define KSZ88_FAMILY_ID			0x88
 #define KSZ8895_FAMILY_ID		0x95
 
-#define KSZ8_PORT_STATUS_0		0x08
+#define KSZ8_PORT_STATUS_0		0x18
 #define KSZ8_PORT_FIBER_MODE		BIT(7)
 
 #define SW_CHIP_ID_M			GENMASK(7, 4)
-- 
2.43.0

Re: [PATCH net] net: dsa: microchip: fix KSZ8765 fiber detection

[netdev-bot+sinfo]

Hi!

This is an automated message. This series looks like a fix, but its
commit messages seem to be missing some information:

 - How the issue was discovered, e.g. hit in production, hit during
   development, syzbot report, manual code inspection, LLM or static
   analysis tool scan.

 - Whether the issue was actually triggered, or is only theoretical
   (e.g. found by code inspection). If it was triggered please include
   the symptoms, like the stack trace or error messages.

Please do not repost the series just to address the above. Instead,
reply to this email with the missing information, so that reviewers
can take it into account. If the series needs another revision for
other reasons, please include the information in the commit messages
then.

The evaluation is done by an LLM so it may be wrong, if you think
that is the case please reply and explain.

Re: [PATCH net] net: dsa: microchip: fix KSZ8765 fiber detection

[Sébastien Royen]

Le 06/10/2026 à 16:20, netdev-bot+sinfo@kernel.org a écrit :
> Hi!
>
> This is an automated message. This series looks like a fix, but its
> commit messages seem to be missing some information:
>
>   - How the issue was discovered, e.g. hit in production, hit during
>     development, syzbot report, manual code inspection, LLM or static
>     analysis tool scan.
>
>   - Whether the issue was actually triggered, or is only theoretical
>     (e.g. found by code inspection). If it was triggered please include
>     the symptoms, like the stack trace or error messages.
>
> Please do not repost the series just to address the above. Instead,
> reply to this email with the missing information, so that reviewers
> can take it into account. If the series needs another revision for
> other reasons, please include the information in the commit messages
> then.
>
> The evaluation is done by an LLM so it may be wrong, if you think
> that is the case please reply and explain.

Hi,

This issue was discovered when upgrading an embedded device from kernel 5.10 to 6.16.

The device was using a KSZ8765 device tree configuration and the
corresponding hardware, but during boot the kernel incorrectly detected
it as a KSZ8795.

The issue was reproduced during testing. The relevant boot messages were:

     ksz-switch spi0.0: found switch: KSZ8795, rev 0
     ksz-switch spi0.0: Device tree specifies chip KSZ8765 but found KSZ8795, please fix it!

The fix was then tested manually.

Thanks,

Re: [PATCH net] net: dsa: microchip: fix KSZ8765 fiber detection

[Andrew Lunn]

> This issue was discovered when upgrading an embedded device from kernel 5.10 to 6.16.

So is this a regression?

If it is, please take a read of:

https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html

and consider if this should be backported to stable.

You then need to set the tree as 'net'

https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html

	Andrew

Re: [PATCH net] net: dsa: microchip: fix KSZ8765 fiber detection

[Nicolai Buchwitz]

Hi Andrew

On October 6, 2026 6:16:02 PM GMT+02:00, Andrew Lunn <andrew@lunn.ch> wrote:
>> This issue was discovered when upgrading an embedded device from kernel 5.10 to 6.16.
>
>So is this a regression?
>
>If it is, please take a read of:
>
>https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
>
>and consider if this should be backported to stable.
>
>You then need to set the tree as 'net'

I might be overlooking something,  but the target tree is already net?

>
>https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html
>
>	Andrew
>

Regards 
Nicolai

Re: [PATCH net] net: dsa: microchip: fix KSZ8765 fiber detection

[Andrew Lunn]

On Tue, Oct 06, 2026 at 06:21:52PM +0200, Nicolai Buchwitz wrote:
> Hi Andrew
> 
> On October 6, 2026 6:16:02 PM GMT+02:00, Andrew Lunn <andrew@lunn.ch> wrote:
> >> This issue was discovered when upgrading an embedded device from kernel 5.10 to 6.16.
> >
> >So is this a regression?
> >
> >If it is, please take a read of:
> >
> >https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> >
> >and consider if this should be backported to stable.
> >
> >You then need to set the tree as 'net'
> 
> I might be overlooking something,  but the target tree is already net?

Oh, yes. Was it a missing Fixes tag which made me think something was
wrong?

	Andrew

Re: [PATCH net] net: dsa: microchip: fix KSZ8765 fiber detection

[Nicolai Buchwitz]

On 6.10.2026 20:24, Andrew Lunn wrote:
> On Tue, Oct 06, 2026 at 06:21:52PM +0200, Nicolai Buchwitz wrote:
>> Hi Andrew
>> 
>> On October 6, 2026 6:16:02 PM GMT+02:00, Andrew Lunn <andrew@lunn.ch> 
>> wrote:
>> >> This issue was discovered when upgrading an embedded device from kernel 5.10 to 6.16.
>> >
>> >So is this a regression?
>> >
>> >If it is, please take a read of:
>> >
>> >https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
>> >
>> >and consider if this should be backported to stable.
>> >
>> >You then need to set the tree as 'net'
>> 
>> I might be overlooking something,  but the target tree is already net?
> 
> Oh, yes. Was it a missing Fixes tag which made me think something was
> wrong?

Yes. It should be

   Fixes: 91a98917a883 ("net: dsa: microchip: move switch chip_id 
detection to ksz_common")

Sébastien, can you please resend the patch with the Fixes tag? With this 
change:

Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>

Thanks
Nicolai

[PATCH net v2] net: dsa: microchip: fix KSZ8765 fiber detection

[Sebastien Royen]

The KSZ8765 is similar to the KSZ8795 but has two fiber ports.

KSZ8_PORT_STATUS_0 is used to detect fiber mode. It is currently
defined as 0x08, which is the Global Control 6 MIB Control register
and has bit 7 defined as Flush Counter.

Set KSZ8_PORT_STATUS_0 to 0x18, which is the Port 1 Status 0 register
where bit 7 is the Fiber Mode bit.

Fixes: 91a98917a883 ("net: dsa: microchip: move switch chip_id detection to ksz_common")
Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>
Signed-off-by: Sebastien Royen <sebastien.royen@armadeus.com>
---
 drivers/net/dsa/microchip/ksz_common.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/dsa/microchip/ksz_common.h b/drivers/net/dsa/microchip/ksz_common.h
index cbe98494578c..f6104f714a8d 100644
--- a/drivers/net/dsa/microchip/ksz_common.h
+++ b/drivers/net/dsa/microchip/ksz_common.h
@@ -853,7 +853,7 @@ static inline bool ksz_is_sgmii_port(struct ksz_device *dev, int port)
 #define KSZ88_FAMILY_ID			0x88
 #define KSZ8895_FAMILY_ID		0x95
 
-#define KSZ8_PORT_STATUS_0		0x08
+#define KSZ8_PORT_STATUS_0		0x18
 #define KSZ8_PORT_FIBER_MODE		BIT(7)
 
 #define SW_CHIP_ID_M			GENMASK(7, 4)
-- 
2.43.0

Re: [PATCH net v2] net: dsa: microchip: fix KSZ8765 fiber detection

[Nicolai Buchwitz]

Hi Sébastien

On 7.10.2026 10:05, Sebastien Royen wrote:
> The KSZ8765 is similar to the KSZ8795 but has two fiber ports.
> 
> KSZ8_PORT_STATUS_0 is used to detect fiber mode. It is currently
> defined as 0x08, which is the Global Control 6 MIB Control register
> and has bit 7 defined as Flush Counter.
> 
> Set KSZ8_PORT_STATUS_0 to 0x18, which is the Port 1 Status 0 register
> where bit 7 is the Fiber Mode bit.
> 
> Fixes: 91a98917a883 ("net: dsa: microchip: move switch chip_id 
> detection to ksz_common")
> Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>
> Signed-off-by: Sebastien Royen <sebastien.royen@armadeus.com>
> ---
>  drivers/net/dsa/microchip/ksz_common.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/dsa/microchip/ksz_common.h 
> b/drivers/net/dsa/microchip/ksz_common.h
> index cbe98494578c..f6104f714a8d 100644
> --- a/drivers/net/dsa/microchip/ksz_common.h
> +++ b/drivers/net/dsa/microchip/ksz_common.h
> @@ -853,7 +853,7 @@ static inline bool ksz_is_sgmii_port(struct 
> ksz_device *dev, int port)
>  #define KSZ88_FAMILY_ID			0x88
>  #define KSZ8895_FAMILY_ID		0x95
> 
> -#define KSZ8_PORT_STATUS_0		0x08
> +#define KSZ8_PORT_STATUS_0		0x18
>  #define KSZ8_PORT_FIBER_MODE		BIT(7)
> 
>  #define SW_CHIP_ID_M			GENMASK(7, 4)

Please do not send new versions in response to the earlier version, but 
send it
like you would send a new patch (with the usual v2 ... prefix).

For more details please have a look at the netdev contribution docs [1]

[1] 
https://docs.kernel.org/process/maintainer-netdev.html#resending-after-review

Thanks,
Nicolai

Re: [PATCH net v2] net: dsa: microchip: fix KSZ8765 fiber detection

[netdev-bot+sinfo]

Hi!

This is an automated message. This series looks like a fix, but its
commit messages seem to be missing some information:

 - How the issue was discovered, e.g. hit in production, hit during
   development, syzbot report, manual code inspection, LLM or static
   analysis tool scan.

 - Whether the issue was actually triggered, or is only theoretical
   (e.g. found by code inspection). If it was triggered please include
   the symptoms, like the stack trace or error messages.

Please do not repost the series just to address the above. Instead,
reply to this email with the missing information, so that reviewers
can take it into account. If the series needs another revision for
other reasons, please include the information in the commit messages
then.

The evaluation is done by an LLM so it may be wrong, if you think
that is the case please reply and explain.

Re: [PATCH net] net: dsa: microchip: fix KSZ8765 fiber detection

[netdev-bot+sashiko]

Thank you for your contribution! Sashiko AI review found 1 potential
issue(s) to consider.

Critical: 0 · High: 0 · Medium: 1 · Low: 0 (1)

If you believe none of the issues are legitimate, please reply to each
issue of Medium severity or higher and explain why the AI is wrong.
If any of them are legitimate and you plan to respin, please let patchwork
know by including "pw-bot: cr" as a separate line at the end of your reply
(one such reply per series is enough).

- [Medium] The patch fixes a long-standing, user-visible misdetection but
  carries no Fixes: tag and no Cc: stable.

Pre-existing issues:
- [Low] In ksz_switch_detect() (ksz_common.c:2927-2933), `u8 val;` is
  declared uninitialized and `ksz_read8(dev, KSZ8_PORT_STATUS_0, &val);`…

--

net: dsa: microchip: fix KSZ8765 fiber detection

This commit changes KSZ8_PORT_STATUS_0 from 0x08 to 0x18, so that
ksz_switch_detect() reads the Port 1 Status 0 register when it checks the
fiber mode bit. The old address was Global Control 6, where bit 7 is the
MIB flush counter bit, so KSZ8765 chips were never identified.

> diff --git a/drivers/net/dsa/microchip/ksz_common.h b/drivers/net/dsa/microchip/ksz_common.h
> index cbe98494578c3..f6104f714a8d1 100644
> --- a/drivers/net/dsa/microchip/ksz_common.h
> +++ b/drivers/net/dsa/microchip/ksz_common.h
> @@ -853,7 +853,7 @@ static inline bool ksz_is_sgmii_port(struct ksz_device *dev, int port)
>  #define KSZ88_FAMILY_ID			0x88
>  #define KSZ8895_FAMILY_ID		0x95
>  
> -#define KSZ8_PORT_STATUS_0		0x08
> +#define KSZ8_PORT_STATUS_0		0x18
>  #define KSZ8_PORT_FIBER_MODE		BIT(7)

[Severity: Medium]
Should this patch carry a Fixes: tag and a Cc: stable? Signed-off-by is
the only trailer at the moment.

With the old value of 0x08, ksz_switch_detect() reads REG_SW_CTRL_6, where
BIT(7) is SW_MIB_COUNTER_FLUSH and not the fiber mode bit. A real KSZ8765
stays detected as KSZ8795_CHIP_ID. ksz_check_device_id() then fails the
probe with -ENODEV, even with a correct "microchip,ksz8765" DT:

ksz_switch_register()
  ksz_switch_detect()
    ksz_read8(dev, KSZ8_PORT_STATUS_0, &val)
  ksz_check_device_id()
    "Device tree specifies chip %s but found %s, please fix it!"

The original driver, commit e66f840c08a237 ("net: dsa: ksz: Add Microchip
KSZ8795 DSA driver"), read REG_PORT_1_STATUS_0 (0x18), which is correct.

The wrong address appears to come from commit 4b20a07e103f ("net: dsa:
microchip: ksz8795: add support for ksz88xx chips"). That commit replaced
the register with the per-port offset REG_PORT_STATUS_0 (0x08) inside the
same global ksz_read8() call.

Commit 91a98917a888 ("net: dsa: microchip: move switch chip_id detection
to ksz_common") then carried 0x08 into the new KSZ8_PORT_STATUS_0 define.

Would something like this fit?

Fixes: 4b20a07e103f ("net: dsa: microchip: ksz8795: add support for ksz88xx chips")
Cc: stable@vger.kernel.org

[Severity: Low]
This is a pre-existing issue that this patch did not introduce. Now that
this read returns a meaningful bit, should ksz_switch_detect() check the
return value of ksz_read8()?

drivers/net/dsa/microchip/ksz_common.c:ksz_switch_detect() {
    ...
		if (id2 == KSZ87_CHIP_ID_95) {
			u8 val;

			dev->chip_id = KSZ8795_CHIP_ID;

			ksz_read8(dev, KSZ8_PORT_STATUS_0, &val);
			if (val & KSZ8_PORT_FIBER_MODE)
				dev->chip_id = KSZ8765_CHIP_ID;
    ...
}

ksz_read8() copies its local value into *val even when regmap_read()
fails:

drivers/net/dsa/microchip/ksz_common.h:ksz_read8() {
	unsigned int value;
	int ret = regmap_read(ksz_regmap_8(dev), reg, &value);
    ...
	*val = value;
	return ret;
}

On a bus error, the choice between KSZ8765 and KSZ8795 is then made from
uninitialized stack data. If that picks the wrong chip,
ksz_check_device_id() returns -ENODEV with the "please fix it!" message
and the real I/O error is lost.

The other reads in this function (REG_CHIP_ID0, REG_KSZ8864_CHIP_ID and
REG_CHIP_ID4) all check ret and return it.

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20261006130006.134847-1-sebastien.royen%40armadeus.com

Re: [PATCH net v2] net: dsa: microchip: fix KSZ8765 fiber detection

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Wed,  7 Oct 2026 10:05:57 +0200 you wrote:
> The KSZ8765 is similar to the KSZ8795 but has two fiber ports.
> 
> KSZ8_PORT_STATUS_0 is used to detect fiber mode. It is currently
> defined as 0x08, which is the Global Control 6 MIB Control register
> and has bit 7 defined as Flush Counter.
> 
> Set KSZ8_PORT_STATUS_0 to 0x18, which is the Port 1 Status 0 register
> where bit 7 is the Fiber Mode bit.
> 
> [...]

Here is the summary with links:
  - [net,v2] net: dsa: microchip: fix KSZ8765 fiber detection
    https://git.kernel.org/netdev/net/c/fc13ba44da19

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
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