linux-kernel - Re: [PATCH v8 2/5] ACPI/PCI: Ignore _OSC negotiation result if pcie_ports

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Date:   Tue, 15 Sep 2020 17:20:33 -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 2/5] ACPI/PCI: Ignore _OSC negotiation result if
 pcie_ports_native is set.

On Sun, Sep 13, 2020 at 01:54:38PM -0700, Kuppuswamy, Sathyanarayanan wrote:
> On 9/10/20 1:14 PM, Bjorn Helgaas wrote:
> > On Fri, Jul 24, 2020 at 08:58:53PM -0700, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
> > > From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> > > 
> > > pcie_ports_native is set only if user requests native handling
> > > of PCIe capabilities via pcie_port_setup command line option.
> > > User input takes precedence over _OSC based control negotiation
> > > result. So consider the _OSC negotiated result only if
> > > pcie_ports_native is unset.
> > > 
> > > Also, since struct pci_host_bridge ->native_* members caches the
> > > ownership status of various PCIe capabilities, use them instead
> > > of distributed checks for pcie_ports_native.
> > > 
> > > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> > > ---
> > >   drivers/acpi/pci_root.c           | 61 ++++++++++++++++++++++++++-----
> > >   drivers/pci/hotplug/pciehp_core.c |  2 +-
> > >   drivers/pci/pci-acpi.c            |  3 --
> > >   drivers/pci/pcie/aer.c            |  2 +-
> > >   drivers/pci/pcie/portdrv_core.c   |  9 ++---
> > >   5 files changed, 56 insertions(+), 21 deletions(-)
> > > 
> > > diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> > > index f90e841c59f5..f8981d4e044d 100644
> > > --- a/drivers/acpi/pci_root.c
> > > +++ b/drivers/acpi/pci_root.c
> > > @@ -145,6 +145,17 @@ static struct pci_osc_bit_struct pci_osc_control_bit[] = {
> > >   	{ OSC_PCI_EXPRESS_DPC_CONTROL, "DPC" },
> > >   };
> 
> > > +		else
> > > +			dev_warn(&bus->dev, "OS overrides %s firmware control",
> > > +			get_osc_desc(OSC_PCI_EXPRESS_NATIVE_HP_CONTROL));
> > 
> > There's got to be a way to write this more concisely.  Maybe something
> > like this?
> > 
> >    #define OSC_OWNER(ctrl, bit, flag) \
> >      if (!(ctrl & bit)) \
> >        flag = 0;
> > 
> >    if (pcie_ports_native)
> >      decode_osc_control(root, "OS forcibly taking over", ~0);
>
> BIT1 and BIT6 does not have PCIe dependency. And BIT7-31 are reserved.
> So we can't force all _OSC bits based on pcie_ports_native value.
> So, IM0, its better to handle PCIe features seperatly.

Yes, we may need to handle a few bits specially.  But we need to
figure out a nicer-looking way of coding this.  It's too cumbersome to
check pcie_ports_native and log a message for every _OSC bit
individually.

> >    else {
> >      ctrl = root->osc_control_set;
> >      OSC_OWNER(ctrl, OSC_PCI_EXPRESS_AER_CONTROL, host_bridge->native_aer);
> >      OSC_OWNER(ctrl, OSC_PCI_EXPRESS_PME_CONTROL, host_bridge->native_pme);
> >      ...
> >    }
> 
> 
> -- 
> Sathyanarayanan Kuppuswamy
> Linux Kernel Developer