[Intel-gfx] [PATCH v5 00/12] Enable GPU switching on pre-retina?MacBook Pro

[Alex Deucher]

On Tue, Mar 15, 2016 at 1:54 PM, Lukas Wunner <lukas at wunner.de> wrote:
> Hi Alex,
>
> On Sat, Mar 05, 2016 at 01:10:56PM -0500, Alex Deucher wrote:
>> Is there any reason to make use of the mux?
>
> Performance (lower latency => no need for framebuffer writes over PCIe),
> improved battery life (no need to use 2 GPUs simultaneously).
>
> Technically you can't just ignore that the mux is there on the MBP
> because the kernel has no control over the GPU used on boot.
> (It's determined by EFI).
>

Is GPU power switching also handled by the mux?  Is it independent of
the display mux?

>
>> > I've heard that the AMD GPU is picky about external monitors and
>> > doesn't recognize them unless they're plugged in at exactly the
>> > right moment, so you may need to retry a couple of times until it
>> > works.
>>
>> Are talking about some issue specific to these muxed apple systems or
>> in general?
>
> Feedback I got from William Brown of Red Hat who tested the GPU switching
> patches on an MBP8,2 and reported that (independently of the patches),
> a display connected with an original Apple DP-to-DVI adapter would only
> be recognized if plugged in at exactly the right moment and in the correct
> order (first adapter, then display). However it doesn't seem to work
> better on OS X.

Sounds like a issue with their adapter.

>
>
>> If you are having issues, please file a bug.
>
> I'm not having issues so can't file a bug. Besides, filing a bug is no
> guarantee that things get fixed. He had opened a bug for GPU switching
> 3 years ago (https://bugs.freedesktop.org/show_bug.cgi?id=61115) and
> nobody did a thing. Obviously whether something gets fixed is a function
> of the perceived importance by maintainers, unless a volunteer comes
> along and does the dirty work.

Well, of course everyone is busy and developers will prioritize
issues.  However, bugs that are not reported have substantially less
chance of getting fixed.

Alex