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

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Message-ID: <53AA33C5.7060501@intel.com>
Date:	Wed, 25 Jun 2014 10:28:21 +0800
From:	"Chen, Tiejun" <tiejun.chen@...el.com>
To:	Zhenyu Wang <zhenyuw@...ux.intel.com>
CC:	daniel.vetter@...ll.ch, jani.nikula@...ux.intel.com,
	airlied@...ux.ie, intel-gfx@...ts.freedesktop.org,
	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, qemu-devel@...gnu.org
Subject: Re: [Intel-gfx] [RFC][PATCH] gpu:drm:i915:intel_detect_pch: back
 to check devfn instead of check class type

On 2014/6/24 10:59, Zhenyu Wang wrote:
> On 2014.06.19 17:53:51 +0800, 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>
>
> This was added historically when supporting graphics device passthrough.
> Looks qemu upstream can't accept multiple ISA bridge and our PCH is always
> on device 31: func0 as far as I know. Looks good to me.
>
> Reviewed-by: Zhenyu Wang <zhenyuw@...ux.intel.com>
>

Thanks for your review.

Do you know when this can be applied?

Tiejun
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