Run-time Platform changes from eglfs to linuxfb

To whom it may concern:

It is rather a question than a bug report.
Our QT5 was built with -gpa 'eglfs' option to use SGX acceleration on several TI omap platforms running Linux. To verify whether we can use the same QT5 build for software rendering, we changed the plugin platform to LinuxFB by setting the environment variable QT_QPA_PLATFORM=linuxfs. We were able to run several QT5 examples such as widgets/painting/affine/affine, , widgets/painting/deform/deform, and widgets/widgets/calculator/calculator. They run well except that none of them took the full screen:
Both affine and deform took about 2/3 of the long and the page is squeezed. For the calculator, it took also 2/3 of screen, but the calculator only appeared at the left-top screen.

We have added some debug trace which indicates that QT5 find the resolution information from dev/fb0 correctly.

"fb res 800x480 virtual 800x480, line_len 3200, bpp 32"

The resolution matches the output from a simple fb-test program.
root@am437x-evm:~# /opt/fb-test
fb-test 1.1.0 (rosetta)
fb res 800x480 virtual 800x480, line_len 3200, bpp 32

Is it OK to change the plugin platform dynamically?
Is the behavior we observed expected?
What else do we need to configure to have full screen FBdev display?
Should we rebuild QT5 with -qpa 'linuxfb' for software rendering?

Your kind assistance will be highly appreciated!

Best regards,

Eric Ruei