Re: [PATCH v4 2/2] pciutils: Decode Compute eXpress Link DVSEC

[Bjorn Helgaas <helgaas@kernel.org>]

On Mon, Apr 13, 2020 at 08:35:26AM -0700, Sean V Kelley wrote:
> Compute eXpress Link[1] is a new CPU interconnect created with
> workload accelerators in mind. The interconnect relies on PCIe
> electrical and physical interconnect for communication via a Flex Bus
> port which allows designs to choose between providing PCIe or CXL.
> 
> This patch introduces basic support for lspci decode of CXL and
> builds upon the existing Designated Vendor-Specific support in
> lspci through identification of a Flex Bus capable Vendor ID.

I don't think this is quite right.  Isn't the Flex Bus ID the
"DVSEC ID" (not the "DVSEC Vendor ID")?

> +static int
> +is_flexbus_cap(struct device *d, int where)
> +{
> +  u32 hdr;
> +  u16 w;
> +
> +  if (!config_fetch(d, where + PCI_DVSEC_HEADER1, 8))
> +    return 0;

And here, I think we need to check the "DVSEC Vendor ID" first, i.e.,
in the log below, I guess we'd look for the Intel Vendor ID (0x8086).

We can only decode the capability if *both* the DVSEC Vendor ID
(HEADER1) and the DVSEC ID (HEADER2) match.

> +  /* Check for Designated Vendor-Specific Flex Bus Capable ID */
> +  hdr = get_conf_long(d, where + PCI_DVSEC_HEADER2);
> +  w = BITS(hdr, 0, 16);
> +  if (w == PCI_DVSEC_FLEXBUS_ID)
> +    return 1;
> +
> +  return 0;
> +}
> +
>  static void
>  cap_dvsec(struct device *d, int where)
>  {
> @@ -947,7 +992,10 @@ show_ext_caps(struct device *d, int type)
>  	    printf("Readiness Time Reporting <?>\n");
>  	    break;
>  	  case PCI_EXT_CAP_ID_DVSEC:
> -	    cap_dvsec(d, where);
> +	    if (is_flexbus_cap(d, where))
> +	      cap_cxl(d, where);
> +	    else
> +	      cap_dvsec(d, where);
>  	    break;
>  	  case PCI_EXT_CAP_ID_VF_REBAR:
>  	    printf("VF Resizable BAR <?>\n");

> +        Capabilities: [e00 v1] CXL Designated Vendor-Specific:
> +                CXLCap: Cache+ IO+ Mem+ Mem HW Init+ HDMCount 1 Viral-
> +                CXLCtl: Cache+ IO+ Mem- Cache SF Cov 0 Cache SF Gran 0 Cache Clean- Viral-
> +                CXLSta: Viral-
> +        Capabilities: [e38 v1] Device Serial Number 12-34-56-78-90-00-00-00

> +e00: 23 00 81 e3 86 80 80 03 00 00 1f 00 03 00 00 00
> +e10: 00 00 00 00 00 00 00 00 00 00 00 00 03 01 00 08
> +e20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> +e30: 00 00 00 00 00 00 00 00 03 00 01 00 00 00 00 90
> +e40: 78 56 34 12 00 00 00 00 00 00 00 00 00 00 00 00