|From:||Russell King <rmk+lkml-AT-arm.linux.org.uk>|
|To:||Takashi Iwai <tiwai-AT-suse.de>|
|Subject:||Re: DMA API issues|
|Date:||Wed, 23 Jun 2004 13:34:23 +0100|
|Cc:||Linus Torvalds <torvalds-AT-osdl.org>, Jeff Garzik <jgarzik-AT-pobox.com>, Matt Porter <mporter-AT-kernel.crashing.org>, Jamey Hicks <jamey.hicks-AT-hp.com>, Ian Molton <spyro-AT-f2s.com>, linux-kernel-AT-vger.kernel.org, greg-AT-kroah.com, tony-AT-atomide.com, david-b-AT-pacbell.net, joshua-AT-joshuawise.com|
On Tue, Jun 22, 2004 at 12:40:45PM +0200, Takashi Iwai wrote: > At Mon, 21 Jun 2004 20:26:39 -0700 (PDT), > Linus Torvalds wrote: > > > > On Mon, 21 Jun 2004, Linus Torvalds wrote: > > > > > > The argument at some point was that some architectures may not even _have_ > > > a "struct page" for DMA memory, since it's not "normal" memory (ie "slow > > > memory" on m68k). However, I thought we all agreed that such a "struct > > > page" could be furnished if that architecture wants so support mmap'ing. > > > > .. which is not to say that we shouldn't have a "pci_mmap_pages()" thing > > _too_. Pretty clearly the easiest interface often is to just map the pages > > at mmap() time, and then we should just have a helper function to do that. > > > > I thought we did one already, but hey, maybe not. > > I don't think we have such. > > Russell has once proposed a similar one (but not pci-specific), and I > believe it makes sense for many drivers. We can hide the > architecture-specific cache handling inside the helper function, too. Ok. So does anyone have any objections if I push the ARM DMA mmap interface upstream, which consists of: /** * dma_mmap_coherent - map a coherent DMA allocation into user space * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices * @vma: vm_area_struct describing requested user mapping * @cpu_addr: kernel CPU-view address returned from dma_alloc_coherent * @handle: device-view address returned from dma_alloc_coherent * @size: size of memory originally requested in dma_alloc_coherent * * Map a coherent DMA buffer previously allocated by dma_alloc_coherent * into user space. The coherent DMA buffer must not be freed by the * driver until the user space mapping has been released. */ int dma_mmap_coherent(struct device *dev, struct vm_area_struct *vma, void *cpu_addr, dma_addr_t handle, size_t size); and a similar one for the ARM-specific "write combining" case (for framebuffers utilising the DMA API)? This was discussed on linux-arch, and the discussion died while trying to settle on a suitable interface through apparant lack of interest. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: 2.6 PCMCIA - http://pcmcia.arm.linux.org.uk/ 2.6 Serial core - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to email@example.com More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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