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    Subject[RFC][PATCH] gpu:drm:i915:intel_detect_pch: back to check devfn instead of check class type
    Date
    Originally the reason to probe ISA bridge instead of Dev31:Fun0
    is to make graphics device passthrough work easy for VMM, that
    only need to expose ISA bridge to let driver know the real
    hardware underneath. This is a requirement from virtualization
    team. Especially in that virtualized environments, XEN, there
    is irrelevant ISA bridge in the system with that legacy qemu
    version specific to xen, qemu-xen-traditional. So to work
    reliably, we should scan through all the ISA bridge devices
    and check for the first match, instead of only checking the
    first one.

    But actually, qemu-xen-traditional, is always enumerated with
    Dev31:Fun0, 00:1f.0 as follows:

    hw/pt-graphics.c:

    intel_pch_init()
    |
    + pci_isa_bridge_init(bus, PCI_DEVFN(0x1f, 0), ...);

    so this mean that isa bridge is still represented with Dev31:Func0
    like the native OS. Furthermore, currently we're pushing VGA
    passthrough support into qemu upstream, and with some discussion,
    we wouldn't set the bridge class type and just expose this devfn.

    So we just go back to check devfn to make life normal.

    Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>
    ---
    drivers/gpu/drm/i915/i915_drv.c | 19 +++----------------
    1 file changed, 3 insertions(+), 16 deletions(-)

    diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
    index 651e65e..cb2526e 100644
    --- a/drivers/gpu/drm/i915/i915_drv.c
    +++ b/drivers/gpu/drm/i915/i915_drv.c
    @@ -417,18 +417,8 @@ void intel_detect_pch(struct drm_device *dev)
    return;
    }

    - /*
    - * The reason to probe ISA bridge instead of Dev31:Fun0 is to
    - * make graphics device passthrough work easy for VMM, that only
    - * need to expose ISA bridge to let driver know the real hardware
    - * underneath. This is a requirement from virtualization team.
    - *
    - * In some virtualized environments (e.g. XEN), there is irrelevant
    - * ISA bridge in the system. To work reliably, we should scan trhough
    - * all the ISA bridge devices and check for the first match, instead
    - * of only checking the first one.
    - */
    - while ((pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, pch))) {
    + pch = pci_get_bus_and_slot(0, PCI_DEVFN(0x1f, 0));
    + if (pch) {
    if (pch->vendor == PCI_VENDOR_ID_INTEL) {
    unsigned short id = pch->device & INTEL_PCH_DEVICE_ID_MASK;
    dev_priv->pch_id = id;
    @@ -462,10 +452,7 @@ void intel_detect_pch(struct drm_device *dev)
    DRM_DEBUG_KMS("Found LynxPoint LP PCH\n");
    WARN_ON(!IS_HASWELL(dev));
    WARN_ON(!IS_ULT(dev));
    - } else
    - continue;
    -
    - break;
    + }
    }
    }
    if (!pch)
    --
    1.9.1


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