linux-kernel - Re: [RFC][PATCH] gpu:drm:i915:intel_detect_pch: back to check devfn instead of check class type

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Message-ID: <53A40198.6020007@intel.com>
Date:	Fri, 20 Jun 2014 17:40:40 +0800
From:	"Chen, Tiejun" <tiejun.chen@...el.com>
To:	daniel.vetter@...ll.ch, jani.nikula@...ux.intel.com,
	airlied@...ux.ie
CC:	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	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

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)
>
--
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