Re: [PATCH] of: property: Create devlink between PCI Host bridge and Root Port suppliers

On Thu, Feb 05, 2026 at 09:50:20AM +0100, Konrad Dybcio wrote:

On 2/5/26 8:06 AM, Manivannan Sadhasivam wrote:

quoted

In the recent times, devicetree started to represent the PCI Host bridge
supplies like PHY in the Root Port nodes as seen in commit 38fcbfbd4207
("dt-bindings: PCI: qcom: Move PHY & reset GPIO to Root Port node"). But
the Host bridge drivers still need to control these supplies as a part of
their controller initialization/deinitialization sequence.

So the Host bridge drivers end up parsing the Root Port supplies in their
probe() and controlled them. A downside to this approach is that the
devlink dependency between the suppliers and Host bridge is completely
broken. Due to this, the driver core probes the Host bridge drivers even if
the suppliers are not ready, causing probe deferrals and setup teardowns in
probe().

These probe deferrals sometime happen over 1000 times (as reported in Qcom
Glymur platform) leading to a waste of CPU resources and increase in boot
time. So to fix these unnecessary deferrals, create devlink between the
Host bridge and Root Port suppliers in of_fwnode_add_links(). This will
allow the driver core to probe the Host bridge drivers only when all Root
Port suppliers are available.

Reported-by: Bjorn Andersson <andersson@kernel.org>
Signed-off-by: Manivannan Sadhasivam <redacted>
---

[...]

This is not 'required' in bindings and device_type="pci" doesn't uniquely
identify root complexes (as can be seen below).. but I suppose this is the
best delimiter we've got

Yeah. There is no way to uniquely identify the Host bridges in DT. So I had to
settle for this.

Maybe I can check for 'device_type', but that will create devlink between switch
port supplies and Root Ports.

Perhaps it could be made 'required'?

Nah. Linux will generate domain numbers on its own. Also, this is a Linux
specific property, so we cannot make it mandatory in dtschema.

- Mani

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