[RFC] drm + i915 DP MST code preview

[Dave Airlie]

On 2 May 2014 18:52, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> On Fri, May 02, 2014 at 02:39:37PM +1000, Dave Airlie wrote:
>> Hi,
>>
>> Branch: http://cgit.freedesktop.org/~airlied/linux/log/?h=drm-i915-mst-support
>>
>> Okay I've gotten this to light up some monitors using -modesetting so it
>> must be ready for an initial posting,
>
> I see that connectors are added/removed dynamically based on branch
> discovery, but I haven't spotted how that is communicated to userspace.
> I was expecting to see a new uevent. Or do you simply want userspace to
> update it lists of connectors on every hotplug event? Is there anyway to
> retrieve the guid so that we can associate the same XID to each branch
> device for the server lifetime? (Is that even a sane idea?) Can we
> detect when a DP dongle is present splitting DVI/VGA using MST but since
> they use different encoders they already falsely appear as unique
> connectors to i915.ko?

I hadn't considered a new hotplug event but I suppose one makes sense
for this actually,
however userspace will still get old school hotplug events anyways as
the connectors transition to connected state.

I'm not sure how much overhead userspace would have calling
drmGetResources on every hotplug it certainly shouldn't be a common
event,

the GUID is only on DP 1.2 devices, so you don't get one for ever
port, also GUIDs are wiped on powerdown on most devices, default GUID
is 0 except where devices have USB hubs as well, so it probably
doesn't make much sense to bother exposing them directly.

I'm not sure about the last question, MST is always active DP
conversion, each port the protocol advertises will appear as a
connector, the protocol doesn't offer much more detail, like my dock
has a DP port and a HDMI port shared on one DP port, depending on what
is plugged in the port is configured different, but it appears as the
same connector.

Dave.