Re: [PATCH v3 9/9] cxl/acpi: Set ACPI's CXL _OSC to indicate CXL1.1 support

Verma, Vishal L
2022-11-10T00:51:10Z

On Wed, 2022-11-09 at 17:35 -0600, Bjorn Helgaas wrote:
> On Wed, Nov 09, 2022 at 11:40:59AM +0100, Robert Richter wrote:
> > From: Terry Bowman <terry.bowman@amd.com>
> >
> > ACPI includes a CXL _OSC support procedure to communicate the available
> > CXL support to FW. The CXL support _OSC includes a field to indicate
> > CXL1.1 RCH RCD support. The OS sets this bit to 1 if it supports access
> > to RCD and RCH Port registers.[1] FW can potentially change it's operation
>
> s/it's/its/
>
> > depending on the _OSC support setting reported by the OS.
> >
> > The ACPI driver does not currently set the ACPI _OSC support to indicate
> > CXL1.1 RCD RCH support. Change the capability reported to include CXL1.1.
>
> Eight instances of "support" above seems like it might be more than
> necessary.
>
> I don't know the history, but OSC_CXL_1_1_PORT_REG_ACCESS_SUPPORT and
> OSC_CXL_2_0_PORT_DEV_REG_ACCESS_SUPPORT seem like sort of weird names
> since they don't match the spec at all ("RCD and RCH Port Register
> Access Supported" and "CXL VH Register Access Supported").

Ah the RCH/RCD and VH terminology was only introduced in the CXL-3.0
spec. When the above defines were added, the spec was at 2.0, and it
used the descriptions: "CXL 1.1 Port Register Access supported", and
"CXL 2.0 Port/Device Register Access supported" (Table 217 in 2.0).

>
> > [1] CXL3.0 Table 9-26 'Interpretation of CXL _OSC Support Field'
> >
> > Signed-off-by: Terry Bowman <terry.bowman@amd.com>
> > Signed-off-by: Robert Richter <rrichter@amd.com>
> > ---
> >  drivers/acpi/pci_root.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> > index c8385ef54c37..094a59b216ae 100644
> > --- a/drivers/acpi/pci_root.c
> > +++ b/drivers/acpi/pci_root.c
> > @@ -492,6 +492,7 @@ static u32 calculate_cxl_support(void)
> >         u32 support;
> >
> >         support = OSC_CXL_2_0_PORT_DEV_REG_ACCESS_SUPPORT;
> > +       support |= OSC_CXL_1_1_PORT_REG_ACCESS_SUPPORT;
> >         if (pci_aer_available())
> >                 support |= OSC_CXL_PROTOCOL_ERR_REPORTING_SUPPORT;
> >         if (IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE))
> > --
> > 2.30.2
> >