Re: [PATCH net-next v5 0/5] Add PCS support for Qualcomm IPQ9574 SoC

From: Lei Wei
Date: Fri May 16 2025 - 07:18:57 EST



On 5/16/2025 9:40 AM, mr.nuke.me@xxxxxxxxx wrote:
On 5/15/25 10:27 AM, Lei Wei wrote:


On 5/15/2025 10:32 AM, Alex G. wrote:
On 5/14/25 11:03, Lei Wei wrote:> On 5/13/2025 6:56 AM, mr.nuke.me@xxxxxxxxx wrote:
On 2/19/25 4:46 AM, Lei Wei wrote:

I tried this PCS driver, and I am seeing a circular dependency in the clock init. If the clock tree is:
     GCC -> NSSCC -> PCS(uniphy) -> NSSCC -> PCS(mii)

The way I understand it, the UNIPHY probe depends on the MII probe. If MII .probe() returns -EPROBE_DEFER, then so will the UNIPHY .probe(). But the MII cannot probe until the UNIPHY is done, due to the clock dependency. How is it supposed to work?

The way I found to resolve this is to move the probing of the MII clocks to ipq_pcs_get().

This is the kernel log that I see:

[   12.008754] platform 39b00000.clock-controller: deferred probe pending: platform: supplier 7a00000.ethernet-pcs not ready
[   12.008788] mdio_bus 90000.mdio-1:18: deferred probe pending: mdio_bus: supplier 7a20000.ethernet-pcs not ready
[   12.018704] mdio_bus 90000.mdio-1:00: deferred probe pending: mdio_bus: supplier 90000.mdio-1:18 not ready
[   12.028588] mdio_bus 90000.mdio-1:01: deferred probe pending: mdio_bus: supplier 90000.mdio-1:18 not ready
[   12.038310] mdio_bus 90000.mdio-1:02: deferred probe pending: mdio_bus: supplier 90000.mdio-1:18 not ready
[   12.047943] mdio_bus 90000.mdio-1:03: deferred probe pending: mdio_bus: supplier 90000.mdio-1:18 not ready
[   12.057579] platform 7a00000.ethernet-pcs: deferred probe pending: ipq9574_pcs: Failed to get MII 0 RX clock
[   12.067209] platform 7a20000.ethernet-pcs: deferred probe pending: ipq9574_pcs: Failed to get MII 0 RX clock
[   12.077200] platform 3a000000.qcom-ppe: deferred probe pending: platform: supplier 39b00000.clock-controller not ready



Hello, thanks for bringing this to our notice. Let me try to understand the reason for the probe failure:

The merged NSSCC DTS does not reference the PCS node directly in the "clocks" property. It uses a placeholder phandle '<0>' for the reference. Please see below patch which is merged.
https://lore.kernel.org/all/20250313110359.242491-6- quic_mmanikan@xxxxxxxxxxx/

Ideally there should be no direct dependency from NSSCC to PCS driver if
we use this version of the NSSCC DTS.

Hence it seems that you may have a modified patch here, and DTS changes have been applied to enable all the Ethernet components including PCS and NSSCC, and NSSCC modified to have a direct reference to PCS? However even in this case, I think the driver probe should work if the drivers are built as modules. Can you please confirm if the NSSCC and PCS drivers are built-in to the kernel and not built as modules

The NSSCC and PCS built-in. I also added the uniphy PCS clocks to the NSSCC in order to expose the issue.

I have a heavily patched tree with PPE driver and EDMA support. That's the final use case in order to support ethernet, right?


Yes, all the drivers are eventually for enabling the Ethernet function
on IPQ9574.


For the case where the drivers are built-in to kernel, and the NSSCC DTS
node has a direct reference to PCS node, we can use the below solution:
[Note that the 'UNIPHY' PCS clocks are not needed for NSSCC clocks
initialization/registration.]

     Enable 'post-init-providers' property in the NSSCC DTS node to mark
    'UNIPHY' PCS as post-initialization providers to NSSCC. This will
     ensure following probe order by the kernel:

     1.) NSSCC driver
     2.) PCS driver.

Please let me know if the above suggestion can help.

I see. Adding the 'post-init-providers' property does fix the circular dependency. Thank you!

I have another question. Do you have a public repository with the unmerged IPQ9574 patches, including, PCS, PPE, EDMA, QCA8084 ?


May I know the source of your PPE/EDMA changes using which this issue
is seen?

I use a mix of upstream submissions, and openwrt patches. As noted, using 'post-init-providers' takes care of the problem.

https://github.com/mrnuke/linux/commits/ipq95xx-devel-20250515/


The openwrt repository contains the unmerged IPQ9574 patches, Although
this version will be updated very soon with latest code(with some fixes), the version of the code in the repo currently is also functional and tested.

https://github.com/CodeLinaro/openwrt/tree/main/target/linux/ qualcommbe/ patches-6.6


Will you be updating a clock example with IPQ9574 + QCA8084 to the repo?

Alex


Yes. We are planning to post the updated version of QCA8084 PHY driver along with the QCA8084 PHY DT example in the DT bindings. This should be available by the next review cycle.


Later once the IPQ PCS driver is merged, we are planning to push the PCS DTS changes, along with an update of the NSSCC DTS to point to the PCS node and mark the "post-init-providers" property. This should work for all cases.

Also, in my view, it is not suitable to move PCS MII clocks get to
"ipq_pcs_get()" because the natural loading order for the drivers
is as below:

1) NSSCC driver
2) PCS driver
3) Ethernet driver.

Additionally, the community is currently working on an infrastructure to
provide a common pcs get method. (Christian and Sean Anderson has been working on this). Therefore, I expect "ipq_pcs_get" to be dropped in the future and replaced with the common pcs get method once this common infra is merged.

That makes sense. Thank you for clarifying.