[PATCH] Revert "vgaarb: Keep adding VGA device in queue"

Daniel Vetter daniel at ffwll.ch
Mon May 13 15:11:24 UTC 2019

On Mon, May 13, 2019 at 12:14:29PM +0200, Michel Dänzer wrote:
> On 2019-05-10 8:01 p.m., Aaron Ma wrote:
> > On 5/10/19 11:46 PM, Michel Dänzer wrote:
> >>> Given that the bug is a bit a mess I think we need to add a bit more
> >>> context here in the commit message. My understanding:
> >>>
> >>> Goal of the revert commit was to make the integrated boot device the
> >>> primary one, if we can't detect which one is the boot device, instead of
> >>> the last one. Which makes some sense.
> >>>
> >>> Now people have relied on the kernel picking the last one, which usually
> >>> is an add-on card, and therefore simply plugging in an add-on card allows
> >>> them to overwrite the default choice. Which also makes sense, and since
> >>> it's the older behaviour, wins.
> >>>
> >>> I think it'd be good to add a comment here that this behaviour has become
> >>> uapi, e.g.
> >>>
> >>> 	/* Add at the front so that we pick the last device as fallback
> >>> 	 * default, with the usual result that plug in cards are preferred
> >>> 	 * over integrated graphics. */
> >>>
> >>> With that (or similar) and more commit message context:
> >> The bug reporter's system doesn't have integrated graphics though, just
> >> two plug-in cards. It's not clear to me yet that their expectation of
> >> Xorg to pick any particular one of them without configuration was justified.
> > 
> > 
> > This code is kind of fail safe.
> > 
> > When in hybrid graphic mode.
> > It should fallback to integrated GPU, which should always be primary fb.
> > So picking 1st (minor PCI ID number) GPU should make more sense.
> > 
> > When with multiple d-GPUs, we can't say which card should be the right
> > one for users when no Xorg conf set.
> > Usually BIOS will set the 1st (minor PCI ID number) d-GPU as primary.
> > So aligning with BIOS setting will be better I think.
> Right. The bug description even says that the card the reporter expected
> Xorg to come up on is the "secondary" card in a PCIe 1x slot (whereas
> the primary is in PCIe 16x). It seems pretty clear that your change
> actually made things better, and the reporter was just relying on the
> previous wrong behaviour. Therefore I resolved the report as not a bug,
> and this patch should be dropped.

Hm I missed that this is about 2 external pci slots. Agreeing with you
reasoning here now, retracting my r-b.
Daniel Vetter
Software Engineer, Intel Corporation

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