Display HP S410u possible workling with RaspberryPi

mlukaszek · 11-03-2016, 01:38 PM

tl;dr: no compatible ARM platform found yet, except for Chromebooks and Android devices.

The main use case we'd like to enable is being able to extend screens - to be able to use multiple monitors simultaneously.

While DisplayLinkManager can be compiled for ARM (and in fact it already has been compiled for ARM; there are Chromebooks which use ARM binary of DLM, as well as our Android app), that's not all you need.

We have not yet seen an ARM based platform which would support cross-device DRM prime support well (necessary to use output offloading, think xrandr --setprovideroutputsource ...). This is required for evdi to get pixels that we display on a device.

Last time I tried, Raspberry Pi was almost there - with Eric Anholt's experimental vc4 module for the GPU. However, I only managed to use one screen at a time - i.e. only DisplayLink-connected screen was operable, not the built-in HDMI. Other devices I tried (e.g. BBB) didn't even get close to this.

You could argue that certain use cases would be fine with just accessing a plain framebuffer through /dev/fbX - so, legacy fbdev interface. Sadly, neither UDL nor evdi don't support this mode anymore - last driver that did was pre-DRM legacy driver "udlfb" - which only supported USB2.0-era devices.

If someone confirms he's successful with second screen driven by UDL on any ARM-based platform, configured in a way that both screens can be used - both the built-in and UDL-driven, I think we'd be happy to release ARM binary of DLM for use with evdi.

Regards,
Michal

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11-03-2016, 01:38 PM	#5
mlukaszek Senior Member Join Date: Feb 2010 Posts: 386	tl;dr: no compatible ARM platform found yet, except for Chromebooks and Android devices. The main use case we'd like to enable is being able to extend screens - to be able to use multiple monitors simultaneously. While DisplayLinkManager can be compiled for ARM (and in fact it already has been compiled for ARM; there are Chromebooks which use ARM binary of DLM, as well as our Android app), that's not all you need. We have not yet seen an ARM based platform which would support cross-device DRM prime support well (necessary to use output offloading, think xrandr --setprovideroutputsource ...). This is required for evdi to get pixels that we display on a device. Last time I tried, Raspberry Pi was almost there - with Eric Anholt's experimental vc4 module for the GPU. However, I only managed to use one screen at a time - i.e. only DisplayLink-connected screen was operable, not the built-in HDMI. Other devices I tried (e.g. BBB) didn't even get close to this. You could argue that certain use cases would be fine with just accessing a plain framebuffer through /dev/fbX - so, legacy fbdev interface. Sadly, neither UDL nor evdi don't support this mode anymore - last driver that did was pre-DRM legacy driver "udlfb" - which only supported USB2.0-era devices. If someone confirms he's successful with second screen driven by UDL on any ARM-based platform, configured in a way that both screens can be used - both the built-in and UDL-driven, I think we'd be happy to release ARM binary of DLM for use with evdi. Regards, Michal