Re: [PATCH v3 03/12] PCI: Move check for old Apple Thunderbolt controllers into a quirk

[Mika Westerberg <mika.westerberg@linux.intel.com>]

Hi,

On Fri, Feb 11, 2022 at 04:06:20PM -0600, Limonciello, Mario wrote:
> On 2/11/2022 15:35, Bjorn Helgaas wrote:
> > On Fri, Feb 11, 2022 at 01:32:41PM -0600, Mario Limonciello wrote:
> > > `pci_bridge_d3_possible` currently checks explicitly for a Thunderbolt
> > > controller to indicate that D3 is possible.  As this is used solely
> > > for older Apple systems, move it into a quirk that enumerates across
> > > all Intel TBT controllers.
> > > 
> > > Suggested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> > > Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> > > ---
> > >   drivers/pci/pci.c    | 12 +++++-----
> > >   drivers/pci/quirks.c | 53 ++++++++++++++++++++++++++++++++++++++++++++
> > >   2 files changed, 60 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > > index 9ecce435fb3f..5002e214c9a6 100644
> > > --- a/drivers/pci/pci.c
> > > +++ b/drivers/pci/pci.c
> > > @@ -1064,7 +1064,13 @@ static inline bool platform_pci_bridge_d3(struct pci_dev *dev)
> > >   	if (pci_use_mid_pm())
> > >   		return false;
> > > -	return acpi_pci_bridge_d3(dev);
> > > +	if (acpi_pci_bridge_d3(dev))
> > > +		return true;
> > > +
> > > +	if (device_property_read_bool(&dev->dev, "HotPlugSupportInD3"))
> > > +		return true;
> > 
> > Why do we need this?  acpi_pci_bridge_d3() already looks for
> > "HotPlugSupportInD3".
> 
> The Apple machines don't have ACPI companion devices that specify this
> property.
> 
> I guess this probes a different question; can `device_property_read_bool` be
> used in `acpi_pci_bridge_d3` instead of:
> 
> 	if (acpi_dev_get_property(adev, "HotPlugSupportInD3",
> 				   ACPI_TYPE_INTEGER, &obj) < 0)
> 		return false;
> 
> 	return obj->integer.value == 1;
> 
> If so, then yeah this can probably be simplified.

Unfortunately the code in acpi_pci_bridge_d3() expects the device to
have an ACPI_COMPANION() which may not be the case with software nodes.

> > 
> > > +	return false;
> > >   }
> > >   /**
> > > @@ -2954,10 +2960,6 @@ bool pci_bridge_d3_possible(struct pci_dev *bridge)
> > >   		if (pci_bridge_d3_force)
> > >   			return true;
> > > -		/* Even the oldest 2010 Thunderbolt controller supports D3. */
> > > -		if (bridge->is_thunderbolt)
> > > -			return true;
> > > -
> > >   		/* Platform might know better if the bridge supports D3 */
> > >   		if (platform_pci_bridge_d3(bridge))
> > >   			return true;
> > > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > > index 6d3c88edde00..aaf098ca7d54 100644
> > > --- a/drivers/pci/quirks.c
> > > +++ b/drivers/pci/quirks.c
> > > @@ -3756,6 +3756,59 @@ DECLARE_PCI_FIXUP_SUSPEND_LATE(PCI_VENDOR_ID_INTEL,
> > >   			       quirk_apple_poweroff_thunderbolt);
> > >   #endif
> > > +/* Apple machines as old as 2010 can do D3 with Thunderbolt controllers, but don't specify
> > > + * it in the ACPI tables
> > 
> > Wrap to fit in 80 columns like the rest of the file.  Also use the:
> > 
> >    /*
> >     * comment ...
> >     */
> > 
> > style if it's more than one line.
> > 
> > I don't think "as old as 2010" is helpful here -- I assume 2010 is
> > there because there *were* no Thunderbolt controllers before 2010, but
> > the code doesn't check any dates, so we basically assume all Apple
> > machines of any age with the listed controllers can do this.
> 
> The old comment was saying that, which is where I got it from.  Yeah, I'll
> update it.
> 
> > 
> > > + */
> > > +static void quirk_apple_d3_thunderbolt(struct pci_dev *dev)
> > > +{
> > > +	struct property_entry properties[] = {
> > > +		PROPERTY_ENTRY_BOOL("HotPlugSupportInD3"),
> > > +		{},
> > > +	};
> > > +
> > > +	if (!x86_apple_machine)
> > > +		return;
> > 
> > The current code doesn't check x86_apple_machine, so this needs some
> > justification.  How do I know this works the same as before?
> 
> Mika and Lucas were saying the only reason for this codepath was Apple
> machines in the first place, which is where this idea came from.

Yes, that's the reason.

Nobody else is going to need this except Apple machines with Intel
Thunderbolt controller.

> Something specifically relevant is that the Apple machines use a SW
> connection manager, whereas everyone else up until USB4 devices use a
> firmware based connection manager with varying behaviors on generation
> (ICM).

Yup.

> > > +
> > > +	if (device_create_managed_software_node(&dev->dev, properties, NULL))
> > > +		pci_warn(dev, "could not add HotPlugSupportInD3 property");
> > > +}
> > > +DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_LIGHT_RIDGE,
> > > +			quirk_apple_d3_thunderbolt);
> > 
> > The current code assumes *all* Thunderbolt controllers support D3, so
> > it would assume a controller released next year would support D3, but
> > this code would assume the opposite.  Are we supposed to add
> > everything to this list, or do newer machines supply
> > HotPlugSupportInD3, or ...?
> 
> This quirk is intended specifically for Apple, which has stopped making
> Intel machines with Intel TBT controllers.
> 
> So I don't believe the list should be growing any more, if anything it might
> need to shrink if I got too many models that weren't actually in Apple
> products.  Lucas probably needs to confirm that.

Yes correct it won't be growing more.