linux-kernel - Re: [PATCH 1/3] PCI: host-common: Add an API to check for any device under the Root Ports

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Message-ID: <znlxzmn74mclx6n3gjz2oordgauygsu5jqs33kc5k34j34b5iq@ntjjj4v7pbpu>
Date: Thu, 6 Nov 2025 17:22:52 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>, 
	lpieralisi@...nel.org, kwilczynski@...nel.org, bhelgaas@...gle.com, will@...nel.org, 
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, robh@...nel.org, 
	linux-arm-msm@...r.kernel.org, zhangsenchuan@...incomputing.com
Subject: Re: [PATCH 1/3] PCI: host-common: Add an API to check for any device
 under the Root Ports

On Thu, Nov 06, 2025 at 10:47:48AM +0100, Konrad Dybcio wrote:
> On 11/6/25 7:13 AM, Manivannan Sadhasivam wrote:
> > Some controller drivers need to check if there is any device available
> > under the Root Ports. So add an API that returns 'true' if a device is
> > found under any of the Root Ports, 'false' otherwise.
> > 
> > Controller drivers can use this API for usecases like turning off the
> > controller resources only if there are no devices under the Root Ports,
> > skipping PME_Turn_Off broadcast etc...
> > 
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
> > ---
> >  drivers/pci/controller/pci-host-common.c | 21 +++++++++++++++++++++
> >  drivers/pci/controller/pci-host-common.h |  2 ++
> >  2 files changed, 23 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
> > index 810d1c8de24e..6b4f90903dc6 100644
> > --- a/drivers/pci/controller/pci-host-common.c
> > +++ b/drivers/pci/controller/pci-host-common.c
> > @@ -17,6 +17,27 @@
> >  
> >  #include "pci-host-common.h"
> >  
> > +/**
> > + * pci_root_ports_have_device - Check if the Root Ports under the Root bus have
> > + *				any device underneath
> > + * @dev: Root bus
> > + *
> > + * Return: true if a device is found, false otherwise
> > + */
> > +bool pci_root_ports_have_device(struct pci_bus *root_bus)
> > +{
> > +	struct pci_bus *child;
> > +
> > +	/* Iterate over the Root Port busses and look for any device */
> > +	list_for_each_entry(child, &root_bus->children, node) {
> > +		if (list_count_nodes(&child->devices))
> 
> Is this list ever shrunk? I grepped around and couldn't find where
> that happens
> 

So I digged into this and other 'pci_bus' lists, to my shock, none of list
entries were getting dropped. I'll send out fixes for all of them.

Thanks for catching this historical issue that no one noticed before :)

- Mani

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