Missing Thunderbolt 3 PCI-E atomics support

[Mika Westerberg]

On Thu, Mar 14, 2019 at 06:54:21PM +0100, Timur Kristóf wrote:
> On Thu, 2019-03-14 at 19:40 +0200, Mika Westerberg wrote:
> > On Thu, Mar 14, 2019 at 06:26:00PM +0100, Timur Kristóf wrote:
> > > I know atomics is a PCIe feature, but in this case the PCIe goes
> > > through TB3, so I would assume it has something to do with it.
> > 
> > Does it work if you plug the graphics card directly to the PCIe slot?
> 
> There is no PCIe slot in which I could plug the graphics card.
> At least I'm not aware of there being one on this laptop.
> Please correct me if I'm wrong.

No, you are right. I forgot that this is a laptop.

> > 
> > > Here is the output of 'lspci -vv':
> > > https://pastebin.com/Qt5RUFVc
> > 
> > The root port (1c.4) says this:
> > 
> >       DevCap2: Completion Timeout: Range ABC, TimeoutDis+, LTR+, OBFF
> > Not Supported ARIFwd+
> > 	   AtomicOpsCap: Routing- 32bit- 64bit- 128bitCAS-
> > 
> > Not knowing much about AtomicOps but to me this looks like the root
> > port
> > does not support the feature.
> 
> What kind of output should lspci show if the feature were supported?

The AMD card has this:

         DevCap2: Completion Timeout: Not Supported, TimeoutDis-, LTR+, OBFF Not Supported
	              AtomicOpsCap: 32bit+ 64bit+ 128bitCAS-

so I would expect something similar on the root port side as
pci_enable_atomic_ops_to_root() fails otherwise with mask of
PCI_EXP_DEVCAP2_ATOMIC_COMP32 | PCI_EXP_DEVCAP2_ATOMIC_COMP64 that the
AMD driver requests.

> As far as I understand the root port is integrated in the CPU, or in
> the chipset maybe? It says it's a Sunrise Point-LP, and I googled it
> but was unable to find a spec sheet.

You can find it here:

  https://www.intel.com/content/www/us/en/products/docs/processors/core/6th-gen-core-pch-u-y-io-datasheet-vol-2.html

Pages 845-826 show the DEVCAP2 register for the 1c.4 (D28/F4) and it
does not seem to have AtomicOps caps set.