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Message-ID: <53A68D1F.5050101@intel.com> Date: Sun, 22 Jun 2014 16:00:31 +0800 From: "Chen, Tiejun" <tiejun.chen@...el.com> To: Daniel Vetter <daniel.vetter@...ll.ch> CC: "Nikula, Jani" <jani.nikula@...ux.intel.com>, Dave Airlie <airlied@...ux.ie>, intel-gfx <intel-gfx@...ts.freedesktop.org>, dri-devel <dri-devel@...ts.freedesktop.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, xen-devel@...ts.xensource.com, qemu-devel@...gnu.org Subject: Re: [RFC][PATCH] gpu:drm:i915:intel_detect_pch: back to check devfn instead of check class type On 2014/6/20 20:32, Daniel Vetter wrote: > Well I have no clue about forwarding the intel gpu to virtualized > hosts and also no idea who could review this really. There's been a > bit a discussion around the iommu mapping forwarding and similar No, this doesn't affect IOMMU mapping. > topics though. So I really wonder how well our driver works in this > use case ... In native case the truth is intel_detect_pch() needs to probe the 00:15.0 to determine what type current pch is, then the i915 driver can be initialized correctly. Actually the 00:15.0 is just a ISA bridge. In virtualized case we thought this ISA bridge mayn't be represented with 00:15.0 originally by qemu-xen-traditional. So instead of checking devfn, the i915 driver check the class type to get this ISA bridge. But with my investigation,qemu-xen-traditional always set 00:15.0 explicitly to represent this ISA bridge. And especially, we wouldn't provide that ISA bridge with an explicit class type in qemu-upstream, so we need to the i915 driver to probe pch by checking devfn. This should work both on the native case and the virtualized case. Thanks Tiejun > -Daniel > > On Fri, Jun 20, 2014 at 11:40 AM, Chen, Tiejun <tiejun.chen@...el.com> wrote: >> Just ping, any comments? >> >> Thanks >> Tiejun >> >> >> On 2014/6/19 17:53, Tiejun Chen wrote: >>> >>> 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@...el.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) >>> >> > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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