On Tue, May 19, 2009 at 9:22 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Tuesday 19 May 2009, FUJITA Tomonori wrote: >> > Would you agree to a patch that works with the same >> > code on e.g. arm, microblaze, mn10300 and sh and >> > uses only a few #ifdefs? >> >> Having such helper for a linear mapping might be helpful but your >> approach is wrong. > > Do you like this approach better? I've merged a few architectures > that were relatively simple. This file should be usable by all > architectures that have a linear mapping and are either fully coherent > (like cris) or just require flushing the dcache when passing a > buffer to the device. I've reviewed the first bit and it looks fine (so far to me). Two related bugs: 1) dma_alloc_coherent() is not respecting the coherent_dma_mask field in device.h:struct device. 2) dma_map_single() is not respecting dma_mask in struct pci_dev (and pointer from struct device). ... > +/** > + * dma_alloc_coherent - allocate consistent memory for DMA > + * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices > + * @size: required memory size > + * @handle: bus-specific DMA address > + * > + * Allocate some uncached, unbuffered memory for a device for > + * performing DMA. This function allocates pages, and will > + * return the CPU-viewed address, and sets @handle to be the > + * device-viewed address. Key here is the DMA is coherent, bi-directional, and the DMA address fit in the coherent_dma_mask. "uncached/unbuffered" is one way of doing this and is how we've implemented "DMA coherency" on parisc platforms that don't have an IOMMU (which all have PA1.1 CPUs) - see arch/parisc/kernel/pci-dma.c And I'll confess pci-dma.c doesn't implement support for coherent_dma_mask . AFAIK, the targeted platforms have < 4GB of RAM and only PCI devices. ISA support is completely missing and is the only case this class of machines need coherent_dma_mask support. More comments on how DMA works for PARISC in arch/parisc/include/asm/dma-mapping.h hth, grant -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
