broadcom-sta-dkms doensn't build against v5.6 mainline kernel: error: implicit declaration of function ‘ioremap_nocache’

DKMS make.log for broadcom-sta-6.30.223.271 for kernel 5.6.0-050600rc5-generic (x86_64)
公曆 20廿年 三月 十日 週二 九時38分49秒
/bin/sh: 1: [: Illegal number:
/bin/sh: 1: [: Illegal number:
Wireless Extension is the only possible API for this kernel version
Using Wireless Extension API
KBUILD_NOPEDANTIC=1 make -C /lib/modules/5.6.0-050600rc5-generic/build M=`pwd`
make[1]: warning: jobserver unavailable: using -j1. Add '+' to parent make rule.
make[1]: Entering directory '/usr/src/linux-headers-5.6.0-050600rc5-generic'
CFG80211 API is prefered for this kernel version
Using CFG80211 API
Kernel architecture is X86_64
  AR /var/lib/dkms/broadcom-sta/6.30.223.271/build/built-in.a
  CC [M] /var/lib/dkms/broadcom-sta/6.30.223.271/build/src/shared/linux_osl.o
/var/lib/dkms/broadcom-sta/6.30.223.271/build/src/shared/linux_osl.c: In function ‘osl_reg_map’:
/var/lib/dkms/broadcom-sta/6.30.223.271/build/src/shared/linux_osl.c:949:10: error: implicit declaration of function ‘ioremap_nocache’; did you mean ‘ioremap_cache’? [-Werror=implicit-function-declaration]
  949 | return (ioremap_nocache((unsigned long)pa, (unsigned long)size));
      | ^~~~~~~~~~~~~~~
      | ioremap_cache
/var/lib/dkms/broadcom-sta/6.30.223.271/build/src/shared/linux_osl.c:949:10: warning: returning ‘int’ from a function with return type ‘void *’ makes pointer from integer without a cast [-Wint-conversion]
  949 | return (ioremap_nocache((unsigned long)pa, (unsigned long)size));
      | ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: some warnings being treated as errors
make[2]: *** [scripts/Makefile.build:268: /var/lib/dkms/broadcom-sta/6.30.223.271/build/src/shared/linux_osl.o] Error 1
make[1]: *** [Makefile:1683: /var/lib/dkms/broadcom-sta/6.30.223.271/build] Error 2
make[1]: Leaving directory '/usr/src/linux-headers-5.6.0-050600rc5-generic'
make: *** [Makefile:177: all] Error 2

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: broadcom-sta-dkms 6.30.223.271-11
Uname: Linux 5.6.0-050600rc5-generic x86_64
ApportVersion: 2.20.11-0ubuntu18
Architecture: amd64
Date: Tue Mar 10 09:50:12 2020
InstallationDate: Installed on 2019-09-28 (163 days ago)
InstallationMedia: Ubuntu 19.10 "Eoan Ermine" - Alpha amd64 (20190923)
PackageArchitecture: all
SourcePackage: broadcom-sta
UpgradeStatus: No upgrade log present (probably fresh install)