Re: [PATCH v3 1/3] xen/igd: get PCH info from host sysfs

Sorry I am not the maintainer/reviewer of Xen IGD passthrough, just out
of my personal interest

On 2026-07-10 02:35, Chuck Zmudzinski wrote:
> The igd_combo_id_infos[] data is more than 10 years
> out of date with many Intel IGD devices missing from
> igd_combo_id_infos[]. This means that many devices
> that could be supported will not work with the
> current implementation.
> 
> For newer devices not listed in igd_combo_id_infos[],
> get infos from the host sysfs to enable support for the
> newer devices not listed in igd_combo_id_infos[].
> 
> Introduce the helper function xen_pt_get_host_pch_info
> to facilitate getting the necessary information from
> sysfs.
> 
> Also, use errp in xen_igd_passthrough_isa_bridge_create
> to set errors from xen_pt_get_host_pch_info.
> 
> Signed-off-by: Chuck Zmudzinski <[email protected]>
> ---
> Changes in v2:
>   - call error_setg* after closing files instead of before closing
>     files
>   - in last line of commit message change "to propagate errors" to
>     "to set errors"
>   - add stable to Cc list
> 
> Changes in v3:
>   - whitespace fix at line 380 of xen_pt_graphics.c
>   - fix Cc address for qemu-stable
> 
>  hw/xen/xen_pt.c          |  2 +-
>  hw/xen/xen_pt_graphics.c | 82 ++++++++++++++++++++++++++++++++++++++--
>  include/hw/xen/xen_igd.h |  3 +-
>  3 files changed, 82 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/xen/xen_pt.c b/hw/xen/xen_pt.c
> index 0fe9c0a..474606e 100644
> --- a/hw/xen/xen_pt.c
> +++ b/hw/xen/xen_pt.c
> @@ -867,7 +867,7 @@ static void xen_pt_realize(PCIDevice *d, Error **errp)
>          }
>  
>          /* Register ISA bridge for passthrough GFX. */
> -        xen_igd_passthrough_isa_bridge_create(s, &s->real_device);
> +        xen_igd_passthrough_isa_bridge_create(s, &s->real_device, errp);

The `errp` need to be handled here if any error occurs.

>      }
>  
>      /* Handle real device's MMIO/PIO BARs */
> diff --git a/hw/xen/xen_pt_graphics.c b/hw/xen/xen_pt_graphics.c
> index 7df9344..2ef941e 100644
> --- a/hw/xen/xen_pt_graphics.c
> +++ b/hw/xen/xen_pt_graphics.c
> @@ -376,8 +376,75 @@ static void pt_graphics_register_types(void)
>  }
>  type_init(pt_graphics_register_types)
>  
> +static void xen_pt_get_host_pch_info(PCIDevice *dev, uint16_t *pch_dev_id,
> +                                     uint8_t *pch_rev_id, Error **errp)
> +{
> +    FILE *fp1, *fp2;
> +    char *endptr;
> +    char device_id[7], rev[5];
> +    size_t len;
> +    const char *device = "/sys/bus/pci/devices/0000:00:1f.0/device";
> +    const char *revision = "/sys/bus/pci/devices/0000:00:1f.0/revision";
> +    unsigned long val;
> +
> +    fp1 = fopen(device, "r");
> +    if (fp1 == NULL) {
> +        error_setg_errno(errp, errno, "Cannot open %s", device);
> +        return;
> +    }
> +    fp2 = fopen(revision, "r");
> +    if (fp2 == NULL) {
> +        fclose(fp1);
> +        error_setg_errno(errp, errno, "Cannot open %s", revision);
> +        return;
> +    }
> +
> +    len = fread(device_id, 1, 7, fp1);
> +    if (!len) {
> +        fclose(fp1);
> +        fclose(fp2);
> +        error_setg(errp, "Cannot read %s", device);
> +        return;
> +    }
> +    len = fread(rev, 1, 5, fp2);
> +    if (!len) {
> +        fclose(fp1);
> +        fclose(fp2);
> +        error_setg(errp, "Cannot read %s", revision);
> +        return;
> +    }
> +    fclose(fp1);
> +    fclose(fp2);
> +
> +    val = strtoul(device_id, &endptr, 16);
> +    if (val > 0xffff) {
> +        error_setg(errp, "PCH device id is out of range: 0x%lx", val);
> +        return;
> +    }
> +    if ((endptr > device_id) && (errno != ERANGE) &&
> +        (errno != EINVAL)) {
> +        *pch_dev_id = (uint16_t)val;
> +    } else {
> +        error_setg_errno(errp, errno, "device id strtoul "
> +                                      "conversion failed");
> +        return;
> +    }
> +    val = strtoul(rev, &endptr, 16);
> +    if (val > 0xff) {
> +        error_setg(errp, "PCH revision is out of range: 0x%lx", val);
> +        return;
> +    }
> +    if ((endptr > rev) && (errno != ERANGE) && (errno != EINVAL)) {
> +        *pch_rev_id = (uint8_t)val;
> +    } else {
> +        error_setg_errno(errp, errno, "revision strtoul "
> +                                      "conversion failed");
> +    }
> +}
> +

It would be better to reuse existing xen_host_pci_device_get() to read host
LPC bridge ids instead of parsing it on our own here.

>  void xen_igd_passthrough_isa_bridge_create(XenPCIPassthroughState *s,
> -                                           XenHostPCIDevice *dev)
> +                                           XenHostPCIDevice *dev,
> +                                           Error **errp)
>  {
>      PCIBus *bus = pci_get_bus(&s->dev);
>      struct PCIDevice *bridge_dev;
> @@ -394,7 +461,16 @@ void xen_igd_passthrough_isa_bridge_create(XenPCIPassthroughState *s,
>          }
>      }
>  
> -    if (pch_dev_id == 0xffff) {
> +    /* Newer devices get PCH infos from host sysfs */
> +    if ((pch_dev_id == 0xffff) || !pch_rev_id) {
> +        xen_pt_get_host_pch_info(&s->dev, &pch_dev_id, &pch_rev_id, errp);
> +    }
> +
> +    XEN_PT_LOG(&s->dev, "PCH device id: 0x%x\n", pch_dev_id);
> +    XEN_PT_LOG(&s->dev, "PCH revision: 0x%x\n", pch_rev_id);
> +
> +    if ((pch_dev_id == 0xffff) || !pch_rev_id) {
> +        error_setg(errp, "failed to get PCH device id or revision");
>          return;
>      }
>  
> @@ -406,7 +482,7 @@ void xen_igd_passthrough_isa_bridge_create(XenPCIPassthroughState *s,
>       * Note that vendor id is always PCI_VENDOR_ID_INTEL.
>       */
>      if (!bridge_dev) {
> -        fprintf(stderr, "set igd-passthrough-isa-bridge failed!\n");
> +        error_setg(errp, "set igd-passthrough-isa-bridge failed!");
>          return;
>      }
>      pci_config_set_device_id(bridge_dev->config, pch_dev_id);
> diff --git a/include/hw/xen/xen_igd.h b/include/hw/xen/xen_igd.h
> index 7ffca06..da51f09 100644
> --- a/include/hw/xen/xen_igd.h
> +++ b/include/hw/xen/xen_igd.h
> @@ -22,7 +22,8 @@ uint32_t igd_read_opregion(XenPCIPassthroughState *s);
>  void xen_igd_reserve_slot(PCIBus *pci_bus);
>  void igd_write_opregion(XenPCIPassthroughState *s, uint32_t val);
>  void xen_igd_passthrough_isa_bridge_create(XenPCIPassthroughState *s,
> -                                           XenHostPCIDevice *dev);
> +                                           XenHostPCIDevice *dev,
> +                                           Error **errp);
>  
>  static inline bool is_igd_vga_passthrough(XenHostPCIDevice *dev)
>  {