Messages in this thread | | | Date | Mon, 27 Oct 2014 12:59:44 +0100 | From | Marek Szyprowski <> | Subject | Re: [PATCH] arm: dma-mapping: fix compilation error when CONFIG_MMU is not present |
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Hello,
On 2014-10-24 15:15, Stefan Hengelein wrote: > Hello, > > adding a dependency to CONFIG_ARM_DMA_USE_IOMMU is probably not a good > idea anyways. > If you read the Documentation/kbuild/kconfig-language.txt, you will see that: > 1. in general, selected options should have no prompt and no dependencies > 2. giving ARM_DMA_USE_IOMMU a dependency on MMU will and cannot solve > the problem, since ARM_DMA_USE_IOMMU itself is selected by several > sources and select will not enforce dependencies to be resolved (to be > precise, it will simply ignore them). Thus, CONFIG_MMU will not be > enabled (as you can see in your warning). > If you want to ensure CONFIG_MMU is enabled when > CONFIG_ARM_DMA_USE_IOMMU is selected, the selecting options (e.g. > SHMOBILE_IOMMU) should have a dependency on MMU. > However, i'm not sure if that's the right way to solve it, since it > will hide these options when MMU is not enabled. > > Making the whole IOMMU subsystem depend on MMU would probably also > solve the problem. Is there any situation where it would make sense to > use an IOMMU without an MMU?
IMHO such configuration doesn't make sense and hiding IOMMU section completely when non-MMU systems are enabled is the right approach.
Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
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