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Commitf263f2a2c6("MIPS: Compile post DMA flush only when needed") pushed the selection of ARCH_HAS_SYNC_DMA_FOR_CPU down to various SYS_HAS_CPU_* Kconfig entries corresponding to CPUs for which cpu_needs_post_dma_flush() might return true, but unfortunately missed the fact that some of these CPUs can be used in configurations with DMA_NONCOHERENT=n. When this is the case the kernel build does not include our definition of arch_sync_dma_for_cpu() from arch/mips/mm/dma-noncoherent.c and the build fails with a link error. One example of this problem is ip27_defconfig: kernel/dma/direct.o: In function `dma_direct_sync_single_for_cpu': direct.c:(.text+0x6c): undefined reference to `arch_sync_dma_for_cpu' kernel/dma/direct.o: In function `dma_direct_sync_sg_for_cpu': direct.c:(.text+0x1f0): undefined reference to `arch_sync_dma_for_cpu' kernel/dma/direct.o: In function `dma_direct_alloc': direct.c:(.text+0xc20): undefined reference to `arch_dma_alloc' kernel/dma/direct.o: In function `dma_direct_free': direct.c:(.text+0xc3c): undefined reference to `arch_dma_free' make[1]: *** [Makefile:1021: vmlinux] Error 1 make: *** [Makefile:152: sub-make] Error 2 Fix this by selecting ARCH_HAS_SYNC_DMA_FOR_CPU only when DMA_NONCOHERENT is also selected. The SYS_HAS_CPU_BMIPS5000 case is left as-is because systems with that CPU always select DMA_NONCOHERENT anyway. Signed-off-by: Paul Burton <paul.burton@mips.com> Fixes:f263f2a2c6("MIPS: Compile post DMA flush only when needed")
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.