The BrightnessContrast effect (and possibly other effects) cause graphical corruption on iMX6 cpus with Vivante GC2000 GPU.

The minimal test case below is enough to trigger the issue.

import QtQuick 2.0
import QtGraphicalEffects 1.0

Rectangle {
    color: "red"
    width: 1024
    height: 768

    BrightnessContrast {
        anchors.fill: parent
        source: parent
        brightness: -0.5
        contrast: -0.1
    }
}

It looks similar to issue 30019, and I've checked that the patches referenced in that bug are already in my Qt version.