We are currently working on a GPU library that can be used to accelerate common image processing algorithms on the imx6. One of the things that we need to do is to transfer the processed data back to the CPU. According to the literature, pbo would be the standard way to do just this. However when trying it on the imx6 with the Vivante driver, the download time is no better than just calling glReadPixels directly without using pbo, which is very slow. Currently we have a way to work around this slow download issue but we would like to know whether this slow pbo read is a bug on the driver implementation or is this due to some other limitation that we are not aware of. Your help on this is appreciated.