[PATCH xserver 1/2] modesetting: Fix swapping of provider sink / source capabilities

[Hans de Goede]

Hi,

On 22-06-16 21:19, Emil Velikov wrote:
> Hi Hans,
>
> On 16 June 2016 at 14:37, Hans de Goede <hdegoede at redhat.com> wrote:
>> When a card has import capability it can be an offload _sink_, not
>> a source and vice versa for export capability.
>>
>> This commit fixes the modesetting driver to properly set these
>> capabilities, this went unnoticed sofar because most gpus have both
>> import and export capability.
>>
> Looking at randr/rrprovider.c ProcRRGetProviderInfo() and the
> randrproto I'm not sure that this patch is correct.
>
> "SourceOffload: This device can source offload buffers"

You should read that as:

"SourceOffload: This device can _be a_ source _of_ offload buffers",
iows it can export buffers,

> My understanding is that such device should have CAP_IMPORT since the
> buffers will be sourced (imported) to the offload GPU to be processed.

No such a device _is_ the offload gpu and can be a source of rendered
buffers for the master to display.

Also see the actual checks for the caps in randr/rrprovider.c
ProcRRSetProviderOffloadSink() :

     if (!(provider->capabilities & RR_Capability_SourceOffload))
         return BadValue;

Where provider is the gpu to which rendering is to be offloaded,
so that one must be able to export images.

And

         if (!(sink_provider->capabilities & RR_Capability_SinkOffload))
             return BadValue;

Where sink_provider is the gpu which has the actual screen attached
(aka the master) and is the one importing the images to display.

Regards,

Hans