dmaengine: fsl-edma: avoid linking both modules

Kbuild does not support having a source file compiled multiple times
and linked into distinct modules, or built-in and modular at the
same time. For fs-edma, there are two common components that are
linked into the fsl-edma.ko for Arm and PowerPC, plus the mcf-edma.ko
module on Coldfire. This violates the rule for compile-testing:

scripts/Makefile.build:236: drivers/dma/Makefile: fsl-edma-common.o is added to multiple modules: fsl-edma mcf-edma
scripts/Makefile.build:236: drivers/dma/Makefile: fsl-edma-trace.o is added to multiple modules: fsl-edma mcf-edma

I tried splitting out the common parts into a separate modules, but
that adds back the complexity that a cleanup patch removed, and it
gets harder with the addition of the tracepoints.

As a minimal workaround, address it at the Kconfig level, by disallowing
the broken configurations.

Link: https://lore.kernel.org/lkml/[email protected]/
Fixes: 66aac8e ("dmaengine: fsl-edma: clean up EXPORT_SYMBOL_GPL in fsl-edma-common.c")
Signed-off-by: Arnd Bergmann <[email protected]>
Acked-by: Peng Fan <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Vinod Koul <[email protected]>

Author: arndb

drivers/dma/Kconfig

@@ -394,7 +394,7 @@ config LS2X_APB_DMA
 
 config MCF_EDMA
 	tristate "Freescale eDMA engine support, ColdFire mcf5441x SoCs"
-	depends on M5441x || COMPILE_TEST
+	depends on M5441x || (COMPILE_TEST && FSL_EDMA=n)
 	select DMA_ENGINE
 	select DMA_VIRTUAL_CHANNELS
 	help