Re: [PATH 0/4] [RFC] Support virtual DRM

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Hi

Am 22.06.21 um 06:02 schrieb Esaki Tomohito:
Hi, Thomas
Thank you for reply.

On 2021/06/21 16:10, Thomas Zimmermann wrote:
Hi

Am 21.06.21 um 08:27 schrieb Tomohito Esaki:
Virtual DRM splits the overlay planes of a display controller into
multiple
virtual devices to allow each plane to be accessed by each process.

This makes it possible to overlay images output from multiple
processes on a
display. For example, one process displays the camera image without
compositor
while another process overlays the UI.

I briefly looked over your patches. I didn't understand how this is
different to the functionality of a compositor? Shouldn't this be solved
in userspace?

I think when latency is important (e.g., AR, VR, for displaying camera
images in IVI systems), there may be use cases where the compositor
cannot be used.
Normally, when the image is passed through the compositor, it is
displayed after 2 VSYNC at most, because the compositor combines the
image with VSYNC synchronization. On the other hand, if we use vDRM, the
image will be displayed at the next VSYNC, so it will be displayed after
1 VSYNC at most.

Other commenters already addressed these points.


Also, since the compositor is a single point of failure, we may not want
to make it dependent on it.

The kernel is also a single point of failure.

TBH I don't think this feature should be merged until there's a clear use case that cannot be solved in userspace idiomatically.

Best regards
Thomas


Best regards
Tomohito Esaki


--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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