Re: [PATCH] drm/i915: refine qemu south bridge detection

From: "Bjørn Mork" <bjorn@mork.no>
To: Jani Nikula <jani.nikula@linux.intel.com>
Cc: David Airlie <airlied@linux.ie>,
	daniel.vetter@ffwll.ch, intel-gfx@lists.freedesktop.org,
	"open list:INTEL DRM DRIVERS (excluding Poulsbo, Moorestow...),
	linux-kernel@vger.kernel.org (open list)"
	<dri-devel@lists.freedesktop.org>,
	Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH] drm/i915: refine qemu south bridge detection
Date: Mon, 25 Jan 2016 10:11:25 +0100	[thread overview]
Message-ID: <87io2inhvm.fsf@nemi.mork.no> (raw)
In-Reply-To: <8760yiukjf.fsf@intel.com> (Jani Nikula's message of "Mon, 25 Jan 2016 10:32:04 +0200")

Jani Nikula <jani.nikula@linux.intel.com> writes:

> On Mon, 25 Jan 2016, Gerd Hoffmann <kraxel@redhat.com> wrote:
>> The test for the qemu q35 south bridge added by commit
>> "39bfcd52 drm/i915: more virtual south bridge detection"
>> also matches on real hardware.  Having the check for
>> virtual systems last in the list is not enough to avoid
>> that ...
>>
>> Refine the check by additionally verifying the pci
>> subsystem id to see whenever it *really* is qemu.
>>
>> Reported-by: Bjørn Mork <bjorn@mork.no>
>> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
>
> Already sent the revert in [1], but I'm fine with this if it works for
> Bjørn.

Gerd's fix works fine for me (of course).  Tested it now just to be 100%
sure, although it was pretty obvious from the code that it would have
the same effect as an revert on my system.

But I have a feeling Gerd might want to send you a v2 of it in any
case...  I was curious about this QEMU subsystem vendor ID, so I went
grepping for it - and found nothing!

 |> +				    pch->subsystem_vendor == 0x1a4f &&
 |> +				    pch->subsystem_device == 0x1100)) {

Looks like a typo:

 bjorn@nemi:/usr/local/src/git/qemu$ git grep PCI_SUBVENDOR_ID_REDHAT_QUMRANET
 hw/pci/pci.c:static uint16_t pci_default_sub_vendor_id = PCI_SUBVENDOR_ID_REDHAT_QUMRANET;
 include/hw/pci/pci.h:#define PCI_SUBVENDOR_ID_REDHAT_QUMRANET 0x1af4

0x1af4 != 0x1a4f

Thanks a lot both of you for a really fast fix.  But it seems Gerd was a
little too fast :)

Bjørn
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