kernel BUG at kernel/sched/deadline ?

Hi,

I am just starting to test a "custom distro" I have made using this kernel and Yocto.
I am facing a "kernel BUG" I cannot understand.

Using:

- kernel 5.4.20-ti-rt-r6 [1fe65cd](https://github.com/beagleboard/linux/commit/1fe65cd99d9e6b466c37ffda016fd65d1f91a0bd) (or 5.4.38-ti-rt-r8 [487bc1d](https://github.com/beagleboard/linux/commit/487bc1d232e6137bb06c363883c5cdc9a5a29bbf))
- defconfig from [ti-linux-rt-5.4.y/patches/defconfig](https://raw.githubusercontent.com/RobertCNelson/ti-linux-kernel-dev/ti-linux-rt-5.4.y/patches/defconfig). The only modifications I have done are unsetting both `CONFIG_MODULE_COMPRESS` and `CONFIG_MODULE_COMPRESS_XZ`
- kernel module omap5-sgx-ddk for GPU support from [https://git.ti.com](https://git.ti.com/cgit/graphics/omap5-sgx-ddk-linux/log/?h=ti-img-sgx/1.17.4948957/k5.4)
- other packages from [meta-ti](https://git.yoctoproject.org/cgit/cgit.cgi/meta-ti/tag/?h=ti2020.00) yocto layer (tag: [ti2020.00](https://git.yoctoproject.org/cgit/cgit.cgi/meta-ti/tag/?h=ti2020.00))
- [BB-BONE-LCD5-01-00A1.dts](https://github.com/beagleboard/bb.org-overlays/blob/master/src/arm/BB-BONE-LCD5-01-00A1.dts)

Hardware:

- BeagleBone green
- a resistive LCD [Seeed-Studio-BeagleBone-Green-LCD-Cape](https://wiki.seeedstudio.com/Seeed-Studio-BeagleBone-Green-LCD-Cape-with-Resistive-Touch/)

When I start Weston touch screen calibration I get:

```
[ 63.286156] 000: kernel BUG at kernel/sched/deadline.c:1495!
[ 63.291842] 000: Internal error: Oops - BUG: 0 [#1] PREEMPT_RT SMP ARM
[ 63.298400] 000: Modules linked in:
[ 63.301902] 000: pvrsrvkm(O)
[ 63.304877] 000: joydev
[ 63.307415] 000: evdev
[ 63.309866] 000:
[ 63.311798] 000: CPU: 0 PID: 644 Comm: weston Tainted: G O 5.4.20 #1
[ 63.319491] 000: Hardware name: Generic AM33XX (Flattened Device Tree)
[ 63.326044] 000: PC is at enqueue_task_dl+0x90/0xd8c
[ 63.331054] 000: LR is at rt_mutex_setprio+0x358/0x568
[ 63.336223] 000: pc : [] lr : [] psr: 20000093
[ 63.342950] 000: sp : da4afa58 ip : da4afb20 fp : da4afb1c
[ 63.348630] 000: r10: df926140 r9 : dc32c420 r8 : 00000001
...
```

Pleased find attached the entire log
[bug_log.txt](https://github.com/beagleboard/linux/files/4664292/bug_log.txt)

Note: attached log has been captured when starting the touch screen calibration, but I got the very same bug with an image without Weston at the end of `ts_calibrate` from [tslib](https://github.com/libts/tslib).

**Considerations**

1. if I use the kernel [linux-ti-staging-rt-5.4](https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/commit/?h=ti-rt-linux-5.4.y&id=27ac613bbce13841a47fcc7341d7c14333b8e0e9) from TI it seems that the issue disappears. Therefore I suppose that I am not configuring this kernel properly.

2. I suppose that the issue is independent form the applications I was runnig and maybe related to some wrong compilation settings (that probably influenced the module pvrsrvkm.ko), but for the moment I am quite clueless.

3. I am not sure that this is worth mentioning but, since the DRM seems to be involved the details about libdrm I am using are:

- https://dri.freedesktop.org/libdrm/libdrm-2.4.99.tar.bz2 with patch [musl-ioctl.patch](https://github.com/openembedded/openembedded-core/blob/zeus/meta/recipes-graphics/drm/libdrm/musl-ioctl.patch)
- I tried *with and without* the patches implemented in [meta-arago](http://arago-project.org/git/?p=meta-arago.git;a=summary) (see TI [pathces](http://arago-project.org/git/?p=meta-arago.git;a=tree;f=meta-arago-distro/recipes-graphics/drm/libdrm;h=6a552a9d28cc1ca86e726465df3bc67ddfa445cd;hb=c8544d7f31c7cbc8f8f1d200cb0b726d03a323d3)) with the *same results*

Any hint would be very appreciated.

Regards
Luca