Hi Michael, >> If an architecture do not support DMA you will get >> a link error: "unknown symbol" for dma_alloc_coherent. > > Yes, it even seems intentional. > But I have a question: can the device work without DMA?
The main dependency is actually on the dma-allocation. In my case I do dma_declare_coherent_memory() with the memory area shared with the remote device as argument. Subsequent calls to dma_alloc_coherent() will then allocate from this memory area. > Does not VIRTIO_CONSOLE_F_DMA_MEM mean dma api is required? Yes.dma_alloc_coherent to work. > If yes you should just fail load. Agree, I'll check on VIRTIO_CONSOLE_HAS_DMA before adding VIRTIO_CONSOLE_F_DMA_MEM to the feature array. > Also let's add a wrapper at top of file so ifdefs > do not litter the code like this. For example: > > #ifdef CONFIG_HAS_DMA > #define VIRTIO_CONSOLE_HAS_DMA (1) > #else > #define VIRTIO_CONSOLE_HAS_DMA (0) > #endif OK, good point. Perhaps we could even exploit gcc's ability to remove dead code and do something like this: if (VIRTIO_CONSOLE_HAS_DMA && virtio_has_feature(vdev, VIRTIO_CONSOLE_F_DMA_MEM)) { ... This does not give any linker warnings when compiling for UML (no DMA). Regards, Sjur _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization