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linux-automation / meta-lxatac

Build your own LXA TAC images and bundles
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meta-lxatac-bsp: linux-lxatac: upgrade to 6.11 #173

Open hnez opened 1 month ago

hnez commented 1 month ago

umpf tag is now: 6.11/customers/lxa/lxatac/20240830-1 The tag includes the following topic branches:

TODO before merging:

hnez commented 1 month ago

I will have to investigate whether the kernel update is actually the root cause here, but the in the bundle I just tested (which includes this kernel update) the tacd crashed with a SIGBUS error in this piece of code:

https://github.com/linux-automation/tacd/blob/a25b8a72e8b7c5d10c2de39190c80b8f77d709f6/src/ui/display.rs#L99-L101

hnez commented 1 month ago

I've just double-checked. The SIGBUS does not occur in Kernel 6.10. It is very unfortunate that 6.11 is already at rc5, because I will be on vacation next week and will not be able to investigate this before the release.

hnez commented 3 weeks ago

I think I have found the offending commit: https://github.com/torvalds/linux/commit/86634fa4e6aeff2e190616c304156899beb4d76b the web version of the diff is not really helpful, but the command line tool shows that the merge commit contains changes which were likely introduced to fix a merge conflict. One of these changes affects drivers/gpu/drm/drm_fbdev_dma.c, which (at least by name) matches the error we see.

Both parents of the merge commit compile and work fine, but the merged version does not (resulting in the previously mentioned SIGBUS error).

hnez commented 2 weeks ago

Thanks to @pH5 we now know why https://github.com/torvalds/linux/commit/86634fa4e6aeff2e190616c304156899beb4d76b is the first commit to expose the problem. It brings together https://github.com/torvalds/linux/commit/9317ff69170d and https://github.com/torvalds/linux/commit/d92a7580392a for the first time.

The first one changes panel-mipi-dbi from being a drm_fbdev_generic device to being a drm_fbdev_dma device. The second one prevents drm_fbdev_dma devices from leaking the memory address of the framebuffer to userspace unless the drm_kms_helper.drm_leak_fbdev_smem=1 kernel commandline option is set.

This being an issue is likely a bug in the panel-mipi-dbi driver that should be fixed there, but this workaround makes sure we can use 6.11 until the driver is fixed.

Thanks again to @pH5 for finding the two commits and the workaround.