linux-kernel - Re: [PATCH v8 1/5] PCI: Conditionally initialize host bridge native

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Date:   Tue, 15 Sep 2020 17:17:21 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, ashok.raj@...el.com
Subject: Re: [PATCH v8 1/5] PCI: Conditionally initialize host bridge
 native_* members

On Sun, Sep 13, 2020 at 01:49:26PM -0700, Kuppuswamy, Sathyanarayanan wrote:
> On 9/10/20 2:00 PM, Kuppuswamy, Sathyanarayanan wrote:
> > On 9/10/20 12:49 PM, Bjorn Helgaas wrote:
> > > On Fri, Jul 24, 2020 at 08:58:52PM -0700, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
> > > > From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> > > > 
> > > > If CONFIG_PCIEPORTBUS is not enabled in kernel then initialing
> > > > struct pci_host_bridge PCIe specific native_* members to "1" is
> > > > incorrect. So protect the PCIe specific member initialization
> > > > with CONFIG_PCIEPORTBUS.
> > > 
> > > s/initialing/initializing/
> > will fix it in next version.
> > > 
> > > > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> > > > ---
> > > >   drivers/pci/probe.c | 4 +++-
> > > >   1 file changed, 3 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > > > index 2f66988cea25..a94b97564ceb 100644
> > > > --- a/drivers/pci/probe.c
> > > > +++ b/drivers/pci/probe.c
> > > > @@ -588,12 +588,14 @@ static void pci_init_host_bridge(struct pci_host_bridge *bridge)
> > > >        * may implement its own AER handling and use _OSC to prevent the
> > > >        * OS from interfering.
> > > >        */
> > > > +#ifdef CONFIG_PCIEPORTBUS
> > > >       bridge->native_aer = 1;
> > > >       bridge->native_pcie_hotplug = 1;
> > > > -    bridge->native_shpc_hotplug = 1;
> > > >       bridge->native_pme = 1;
> > > >       bridge->native_ltr = 1;
> > > 
> > > native_ltr isn't dependent on PCIEPORTBUS either, is it?  It's only
> > > used for ASPM.
> > Agreed. I was confused due to a comment in include/linux/pci.h
> > 
> >   unsigned int    native_ltr:1;           /* OS may use PCIe LTR */

> Currently there is no code dependency between LTR and CONFIG_PCIEPORTBUS.
> 
> But I am wondering whether its correct to move LTR code under
> CONFIG_PCIEPORTBUS?. As per PCIe spec v5.0 sec 7.8.2, LTR is a
> optional PCIe extended capability. So why is not moved under
> drivers/pci/pcie/*. What is the criteria for code to be placed under
> drivers/pci/pcie/*

Some folks think drivers/pci/pcie/ should not exist, and I tend to
agree, but it's a fair bit of churn to remove it.  We do have quite a
bit of PCIe extended capability support in drivers/pci -- ats.c,
iov.c, vc.c.

There's no need to move LTR under CONFIG_PCIEPORTBUS because
CONFIG_PCIEPORTBUS enables portdrv, and AFAIK there's nothing
LTR-related that relies on portdrv.

The stuff currently in drivers/pci/pcie is mostly just portdrv and
services that depend on it.  aspm.c and ptm.c are exceptions and
really should be in drivers/pci.

> > > >       bridge->native_dpc = 1;
> > > > +#endif
> > > > +    bridge->native_shpc_hotplug = 1;
> > > >       device_initialize(&bridge->dev);
> > > >   }
> > > > -- 
> > > > 2.17.1
> > > > 
> > 
> 
> -- 
> Sathyanarayanan Kuppuswamy
> Linux Kernel Developer