[Buildroot] Camera Driver doesn't provide 60 FPS

[Gerd Kautzmann]

>> Gerd Kautzmann <G.Kautzmann at PRIMES.de> wrote:

>> I finally managed to build an linux image suporting my imx296 camera 
>> on the Raspberry-Pi 4 (32 bit) over loadable kernel modules. 
>> ... 
>> Are there any ideas about settings in the configuration concerning 
>> cameras I might have missed?

> Thomas Petazzoni <thomas.petazzoni at bootlin.com>

> This really isn't a Buildroot-related question, so I'm not sure this mailing list is the most 
> relevant place to get support on this question. It's really a RaspberryPi-specific question.

I did some tests with Yocto and the results where even worse.

But after more checking and testing it might be driver related or related to some DMA settings fort he driver.

Test programs like ' v4l2-ctl --stream-mmap ' are reporting nearly 60fps on Buildroot, Yocto and Raspi-OS.

But when it comes to applications I got differences. 

My test programm is written like:

while(1)
{
   VideoCapture();
   DoSomething();
}

On Raspi-OS  I got 60fps, on Buildroot it does only 30fps with DoSomething() and 60fps without.
It seems the loop has to wait for the end oft he video DMA with Buildroot, where the DMA on Raspi-OS doesn't use CPU time.

So if no one has an idea, this information might be useful for others.