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

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Message-ID: <CAL_JsqLgTriMgQaL_Nbi72nOD=AFdHggKXs3RkKA0UzzChhTUQ@mail.gmail.com>
Date: Mon, 9 Feb 2026 12:26:59 -0600
From: Rob Herring <robh@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
Cc: Konrad Dybcio <konrad.dybcio@....qualcomm.com>, saravanak@...nel.org, 
	andersson@...nel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	qiang.yu@....qualcomm.com
Subject: Re: [PATCH] of: property: Create devlink between PCI Host bridge and
 Root Port suppliers

On Thu, Feb 5, 2026 at 3:01 AM Manivannan Sadhasivam
<manivannan.sadhasivam@....qualcomm.com> wrote:
>
> On Thu, Feb 05, 2026 at 09:50:20AM +0100, 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@...nel.org>
> > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@....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
> >
>
> 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.

You can also check the parent is not PCI to exclude that case.

Rob