linux-kernel - Re: [PATCH] radeon: Test for PCI root bus before assuming bus->self

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Message-ID: <CADnq5_MG2savPeRfUQ-pojCY=jVsvZVBO0TVGJ1LjhKxqR08nA@mail.gmail.com>
Date:	Wed, 27 Aug 2014 22:18:13 -0400
From:	Alex Deucher <alexdeucher@...il.com>
To:	Dave Airlie <airlied@...il.com>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	"Deucher, Alexander" <alexander.deucher@....com>,
	Christian Koenig <christian.koenig@....com>,
	Maling list - DRI developers 
	<dri-devel@...ts.freedesktop.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] radeon: Test for PCI root bus before assuming bus->self

On Wed, Aug 27, 2014 at 9:32 PM, Dave Airlie <airlied@...il.com> wrote:
>> On Wed, Aug 27, 2014 at 3:01 PM, Alex Williamson
>> <alex.williamson@...hat.com> wrote:
>>> If we assign a Radeon device to a virtual machine, we can no longer
>>> assume a fixed hardware topology, like the GPU having a parent device.
>>> This patch simply adds a few pci_is_root_bus() tests to avoid passing
>>> a NULL pointer to PCI access functions, allowing the radeon driver to
>>> work in a QEMU 440FX machine with an assigned HD8570 on the emulated
>>> PCI root bus.
>>>
>>> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
>>
>
> Does this mean inside a VM we can't enable pcie 2 speeds?
>
> This could lead to a quite disappointing speed decrease for DMA transfers.

It depends on the sbios, but most boards negotiate the highest speed at boot.

Alex
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