Re: Missing Thunderbolt 3 PCI-E atomics support

["Timur Kristóf" <timur.kristof@gmail.com>]

On Thu, 2019-03-14 at 20:17 +0200, Mika Westerberg wrote:
> > > > 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.

This would be the 8th gen (8550U) but I assume it has similar
capabilities to the 6th gen. So, it seems that this is a hardware
limitation of the chipset.

Thanks Mika for clearing that up.

Best regards,
Tim

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