LVGL V9 and framebuffer - image is tearing but didn't with LVGL V8

[TimJTi]

With LVGL V8, before the NuttX upgrade to V9, I was able to use /dev/fb0 successfully and the LVGL demos ran nicely. I could run my own graphic apps too and they behaved. Note - this is with the framebuffer drivers, so LV_USE_NUTTX_LCD is NOT set, and LVGL defaults to opening /dev/fb0.

Since the update to V9 - and with no other changes I can find - even simple graphics, such as a black background with just a spinner, show breakup/tearing with the rendered image.

The example framebuffer app runs seems to just fine (I modified it to draw continuously and tried different delays between drawing the rectangles), so I am fairly sure this is down to the way LVGL now interacts with NuttX (using the master branch).

I initially thought it was lack of double buffers, but comparing lvgl8 and lvgl9 framebuffer code I now not sure there are any difference as I don't think double buffering will be used in either lvgl version: the (SAMA5D2) LCD setup does not specify any virtual x or y values which is what triggers the setting up of a second framebuffer as best as I can tell.

I am happy to investigate further and try things, but I have run out of ideas as to where to look. I posted a similar report to this on the LVGL forum but no one has answered there in 3 days.

For now, I will have to go back to LVGL V8 which is a shame, especially if V9 can be made to work given the amount of rewrite of app code that's needed between the two lvgl versions (annoying!!).

Can anyone help?