On 1/21/2013 9:00 PM, Geert Uytterhoeven wrote:
On Tue, Jan 15, 2013 at 5:56 PM, James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote: > On Tue, 2013-01-15 at 15:07 +0100, Marek Szyprowski wrote: >> On 1/15/2013 10:13 AM, Geert Uytterhoeven wrote: >> > Marek? >> > >> > On Tue, Jan 15, 2013 at 5:16 AM, Vineet Gupta >> > <Vineet.Gupta1@xxxxxxxxxxxx> wrote: >> > > On Monday 14 January 2013 09:07 PM, Mark Salter wrote: >> > >> On Sun, 2013-01-13 at 11:44 +0100, Geert Uytterhoeven wrote: >> > >>> c6x/allmodconfig (assumed): >> > >>> >> > >>> drivers/media/v4l2-core/videobuf2-dma-contig.c: In function ‘vb2_dc_mmap’: >> > >>> drivers/media/v4l2-core/videobuf2-dma-contig.c:204: error: implicit declaration of function ‘dma_mmap_coherent’ >> > >>> drivers/media/v4l2-core/videobuf2-dma-contig.c: In function ‘vb2_dc_get_base_sgt’: >> > >>> drivers/media/v4l2-core/videobuf2-dma-contig.c:387: error: implicit declaration of function ‘dma_get_sgtable’ >> > >>> >> > >>> For architectures using dma_map_ops, dma_mmap_coherent() and >> > >>> dma_get_sgtable() are provided in <asm-generic/dma-mapping-common.h>. >> > >>> >> > >>> C6x does not use dma_map_ops, hence it should implement them as inline >> > >>> stubs using dma_common_mmap() and dma_common_get_sgtable(). >> > >>> >> > >> So are dma_mmap_coherent() and dma_get_sgtable() part of the DMA API >> > >> now? I don't them in Documentation/DMA*.txt anywhere. >> > >> >> > >> Why does the default dma_common_mmap() for !CONFIG_MMU return an >> > >> error? >> > >> >> > >> Wouldn't it be better to provide default implementations that an arch >> > >> could override rather than having to patch all "no dma_map_ops" >> > >> architectures? >> > >> >> > > Speaking for the still-reviewed ARC Port, I completely agree with Mark. >> >> dma_mmap_coherent() was partially in the DMA mapping API for some time, but >> it was available only on a few architectures (afair ARM, powerpc and avr32). >> This caused significant problems for writing unified device drivers or some >> device helper modules which were aimed to work on more than one >> architecture. >> >> dma_get_sgtable() is an extension discussed during the Linaro meetings. It >> is required to correctly implement buffer sharing between device driver >> without hacks or any assumptions about memory layout in the device drivers. >> >> I have implemented some generic code for both of those two functions, >> keeping >> in mind that on some hardware architectures (like already mentioned VIVT) >> it might be not possible to provide coherent mapping to userspace. It is >> perfectly fine for those functions to return an error in such case. > > It's not possible on VIPT either. This means that the API is unusable > on quite a large number of architectures. Surely, if we're starting to > write drivers using this, we need to fix the API before more people try > to use it. > > For PA-RISC (and all other VIPT, I assume) I need an API which allows me > to remap the virtual address of the kernel component (probably using the > kmap area) so the user space and kernel space addresses are congruent. So what are we gonna do for 3.8? I'd like to get my allmodconfig build green again ;-) Change the API? Keep the API but do a best-effort fix to unbreak the builds? - Apply my patches that got acks (avr32/blackfin/cris/m68k), - Use static inlines that return -EINVAL for the rest (c6x/frv/mn10300/parisc/xtensa). I still have a few m68k fixes queued for 3.8, for which I've been postponing the pull request to get this sorted out, so I could include the above.
I think this would be the best solution for fixing v3.8. I would like to put those patches in linux-next asap and then after a week or so send a pull request for merging them to v3.8-rc6. EINVAL approach can be later fixed/extended with real implementation (if there are any driver candidates, which will use such interface). Best regards -- Marek Szyprowski Samsung Poland R&D Center -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
