Den 29.04.2020 14.48, skrev Noralf Trønnes: > Hi, > > A while back I had the idea to turn a Raspberry Pi Zero into a $5 > USB to HDMI/SDTV/DSI/DPI display adapter. > > This series adds a USB host driver and a device/gadget driver to achieve > that. > > The reason for calling it 'Generic' is so anyone can make a USB > display/adapter against this driver, all that's needed is to add a USB > vid:pid. I was hoping to have someone working on a microcontroller based > USB display by now, but unfortunately that has been delayed. It would > have been nice to have a microcontroller implementation to ensure that I > haven't made things unnecessary difficult to implement. > > Performance > The one thing that decides how useful this all is, is how smooth an > experience it gives. My hope was that it should not be noticeably laggy > with ordinary office use on 1920x1080@RG16. I'm pleased to see that it's > also possible to watch youtube movies, although not in fullscreen. > > Some of the main factors that affects performance: > - Display resolution > - Userspace providing damage reports (FB_DAMAGE_CLIPS or > DRM_IOCTL_MODE_DIRTYFB) > - Color depth (DRM_CAP_DUMB_PREFERRED_DEPTH = 16 if RGB565) > - How well the frames compress (lz4) > - Gadget device memory bandwidth, CPU power for decompression > - (Big endian hosts will have to do byte swapping on the frames) One factor that I forgot is USB2 vs USB3. The Pi's have a USB2 Device controller (dwc2). I couldn't find a cheap board with a USB3 Device controller that could run mainline Linux, so I haven't tried that. > > I've tested these: > - xorg-server on Pi4. This was nice and smooth since it uses > DRM_IOCTL_MODE_DIRTYFB and honours DRM_CAP_DUMB_PREFERRED_DEPTH. > - Ubuntu 20.04 GNOME on x86. This was useable, but not so good for > movies. GNOME doesn't look at DRM_CAP_DUMB_PREFERRED_DEPTH and doesn't > set FB_DAMAGE_CLIPS on the pageflips. > > I've made a short video to show what it looks like[1]. I got a question if this would work with usbip[4], USB over IP. I did a quick test with two Pi4's connected by cable to the same network switch (1Gb). Showing a movie in a window like my previous test didn't show much of a difference. Maybe some occasional glitching, hard to tell without proper tests. There's no pageflipping on the device side, so it could be tearing that I saw. Noralf. [4] tools/usb/usbip/README > > I have used a Pi4 as the gadget during development since it has much > better memory bandwith (4000 vs 200 MBps)[2] and CPU than the PiZ. They > both have the same gadget controller (dwc2). > > I did an RFC [3] of this 2 months ago where I looked at doing a Multi > Function USB device. I gave up on that when I realised how much work the > review process would be. So I stripped down to my original idea. I have > made sure that the drivers will tolerate another USB interface of type > VENDOR, so it's still possible for the display to be part of a multi > function device. > > Noralf. > > [1] https://youtu.be/AhGZWwUm8JU > [2] https://magpi.raspberrypi.org/articles/raspberry-pi-specs-benchmarks > [3] https://patchwork.freedesktop.org/series/73508/ > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
