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 9:50 AM, Konrad Dybcio wrote:
> 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'?

I cut out the line where it said:

if (of_property_present(con_np, "linux,pci-domain")) {

Konrad
> 
> 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;
>>  }