Re: [linux-next:master 4238/6654] include/linux/dmaengine.h:1576: undefined reference to `dma_request_chan'

Tuesday, 15 September 2020

Hi Nathan,

On 11/09/2020 18.54, Nathan Chancellor wrote:
...
 For what it's worth, I can reproduce this failure at that
particular
 commit and I see a Kconfig warning along with it:

 WARNING: unmet direct dependencies detected for DMA_ENGINE
   Depends on [n]: DMADEVICES [=n]
   Selected by [m]:
   - DRM_ZYNQMP_DPSUB [=m] && HAS_IOMEM [=y] && (ARCH_ZYNQMP [=y] ||
COMPILE_TEST [=n]) && COMMON_CLK [=y] && DRM [=y] && OF [=y]

 However, at tip of -next, the config is fine. It appears this is fixed
 with the commit that fixes that warning:

 https://git.kernel.org/next/linux-next/c/3e8b2403545efd46c6347002e27eae47... 
Right, this is fixing the incorrect config.
Without DMADEVICES the drivers/dma is not going to be built, and the
header (include/linux/dmaengine.h) checks for CONFIG_DMA_ENGINE to
decide if the drivers/dma/dmaengine.o is built or not.

In the failure we have
DMADEVICES=n
DMA_ENGINE=y

yet, the dmaengine is not built as the whole drivers/dma/ is skipped.

Interesting case.
If we make DMA_ENGINE to depend on DMADEVICES then this should not
happen (and also DMA_ACPI and DMA_OF ?)

- Péter

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