Advanced users • Re: Moving Linux Kernel to 6.6

Hi all, apologies if this is the wrong place to post.

I’ll preface this by saying I’m relatively new to Linux, so please feel free to call out any glaring mistakes.

It seems there’s a bug in the 6.6 kernel that affects the Raspberry Pi 3B+ and older models. As far as I can tell, this issue hasn’t received much attention. The bug appears to be with v4l2, and it manifests in the HyperHDR package, where colors almost appear inverted when captured via a USB 2.0 HDMI grabber. You can find the full discussion here: https://github.com/awawa-dev/HyperHDR/discussions/848

One suggested solution is to downgrade the kernel, but that doesn’t feel like the most robust fix, in my opinion. I wanted to raise this issue here in hopes of getting it addressed. In the meantime, I’m planning to downgrade to the latest 6.1 LTS kernel, which I believe is version 6.1.77, published on Feb 8th https://github.com/raspberrypi/rpi-firm ... 184527ae3f

I'm not aware of this ever having been reported to us.
Ideally we need to track down roughly when this broke, however as it's now quite a long time back (we're now working against 6.12!) that would take a while. We also need a fair amount more information - assume we know nothing about the setup required for HyperHDR (as we're likely not to), so specifically which USB capture device are you using?

One thought is that on Pi3 you may have switched from a 32bit kernel to a 64bit one. 32bit kernels use the dwc_otg USB driver, whilst 64bit kernels use dwc2. The output of "uname -a" on a good vs bad system would be a good start.
I also see a report in https://github.com/awawa-dev/HyperHDR/d ... nt-9665719 that both 6.6.20 and 6.6.31 work fine (and the version strings both list -v8+ which would be 64bit).

If it is down the the V4L2 saturation, brightness, contrast, and hue controls having taken on weird values, then that is very strange. Those are all defined by the UVC (USB Video Class) spec, and will be common across all platforms.

However, I’m concerned about security. Despite 6.1 being labeled "long-term support," it hasn’t received an update in quite some time, whereas 6.6 has been getting frequent updates. Am I misunderstanding this? Could it simply be that no security patches have been necessary for 6.1 since then?

Mainline keep LTS kernels alive for a defined timescale. Raspberry Pi only keep the latest LTS release supported, hence when 6.6 became our stable kernel the development on 6.1 stopped.

Statistics: Posted by 6by9 — Tue Dec 31, 2024 7:18 pm

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