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

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 2/5/26 8:06 AM, Manivannan Sadhasivam wrote:
> 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 <manivannan.sadhasivam@oss.qualcomm.com>
> ---

[...]

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

Perhaps it could be made 'required'?

Konrad

> +		for_each_available_child_of_node_scoped(con_np, child) {
> +			if (of_node_is_type(child, "pci")) {
> +				for_each_property_of_node(child, p)
> +					of_link_property(child, con_np, p->name);
> +			}
> +		}
> +	}
>  
>  	return 0;
>  }