[Nouveau] [PATCH v3 0/4] nouveau RPM fixes for Optimus (final)

[Alex Deucher]

On Fri, Jul 15, 2016 at 12:31 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> On Fri, Jul 15, 2016 at 12:27 PM, Alex Deucher <alexdeucher at gmail.com> wrote:
>> On Fri, Jul 15, 2016 at 12:10 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>>> On Fri, Jul 15, 2016 at 9:12 AM, Peter Wu <peter at lekensteyn.nl> wrote:
>>>> Hi,
>>>>
>>>> Here are two patches to fix an issue reported on kernel bugzilla (infinite loop
>>>> due to unchecked function) and a more important fix to fix hanging Optimus
>>>> machines when runtime PM is enabled (with pm/pci patches).
>>>>
>>>> These are the final patches targeting v4.8. Changes compared to v2[1]:
>>>> collected R-b from Hans and Mika and fixed a minor comment style issue.
>>>>
>>>> I recommend it to be merged before the pci/pm patches[2], otherwise there is a
>>>> window where newer Nvidia Optimus laptops might fail to runtime resume and/or
>>>> lock up.  Once the pci/pm branch is merged I will propose another patch to
>>>> improve reliability[3].
>>>>
>>>> Known issue with patch 4: when a Nvidia HDMI audio function is present, the
>>>> bridge will not suspend and hence the Nvidia card will still be powered. Fixing
>>>
>>> That's basically all optimus gpu's, right? Anything GT21x+ has a HDMI
>>> audio subfunction, and prior to that, the nvidia gpu tended to be the
>>> only gpu, or hard-muxed.
>>
>> I'd imagine there is a strap on the asic so the audio function is only
>> enabled if there is a connector actually wired to the dGPU.  It
>> doesn't make much sense to expose audio if there is no way to use it.
>
> A lot of the time, there actually is a connector wired up. A lot of
> the other time, there is no connector, but the display unit is still
> there. Very recently, NVIDIA gpu's have started coming out marked as
> "3d accelerator", which sometimes but not always means that there's no
> display unit, and for those, I would assume there is no audio
> subfunction.
>

Just because there is a display block, doesn't mean the audio function
is always enabled.  I suspect it is disabled by hardware straps on
systems with no display connectors or other specific OEM configs.

Alex