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

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Message-ID: <CAL_JsqLBRXj7oqV6qiGjKG05fiQ=AQq1fPhG9dF6D83Lhhd7qQ@mail.gmail.com>
Date: Mon, 9 Feb 2026 12:20:34 -0600
From: Rob Herring <robh@...nel.org>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>, Saravana Kannan <saravanak@...nel.org>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>, 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 Mon, Feb 9, 2026 at 4:38 AM Konrad Dybcio
<konrad.dybcio@....qualcomm.com> wrote:
>
> On 2/8/26 2:27 AM, Saravana Kannan wrote:
> > On Thu, Feb 5, 2026 at 1:01 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>
> >>>> ---
> >>
> >
> > 100% NACK to this patch. You are touching a core part of the
> > fw_devlink code to fix it for one specific case. This is not the place
> > to special case for a property or a framework.

Save NACKs for people that aren't listening and you are done
explaining your objections.


> I think the issue runs deeper. There are multiple cases where an
> OF node has children which represents sub-blocks of a hw block, and
> those may house e.g. a phy reference within. I'm not sure the code can
> handle this today.

Other cases would probably be for very specific bindings, so they
really have to be located with the code for that binding. It wouldn't
scale in the DT code. I'm not all that against this case (PCI handling
is already somewhat mixed in), but if it has to be solved anyways
there's not much reason to handle a subsystem specific case in the DT
code either.

Rob