Messages in this thread | | | Date | Tue, 24 May 2011 16:18:11 +0200 | Subject | Re: mmap() implementation for pci_alloc_consistent() memory? | From | Leon Woestenberg <> |
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Hello Clemens,
On Mon, May 23, 2011 at 10:30 AM, Clemens Ladisch <clemens@ladisch.de> wrote: > Leon Woestenberg wrote: >> Having dma_mmap_coherent() there is good for one or two archs, but how >> can we built portable drivers if the others arch's are still missing? > > Easy: Resolve all issues, implement it for all the other arches, and add > it to the official DMA API. > >> How would dma_mmap_coherent() look like on x86? > > X86 and some others are always coherent; just use vm_insert_page() or > remap_page_range(). > Hello Clemens,
On Mon, May 23, 2011 at 10:30 AM, Clemens Ladisch <clemens@ladisch.de> wrote: > Leon Woestenberg wrote: >> Having dma_mmap_coherent() there is good for one or two archs, but how >> can we built portable drivers if the others arch's are still missing? > > Easy: Resolve all issues, implement it for all the other arches, and add > it to the official DMA API. > I could send patches, but I would get bashed. Would be a learning experience though (and a long email thread).
>> How would dma_mmap_coherent() look like on x86? > > X86 and some others are always coherent; just use vm_insert_page() or > remap_page_range(). >
For x86 (my current test system) I tend to go with remap_page_range() so that the mapping is done before the pages are actually touched.
With that I leave the work-in-progress (dma_mmap_coherent) aside for a moment, I'll revisit that later on ARM.
However, I still feel I'm treading sandy waters, not familiar enough with the VM internals.
Does memory allocated with pci_alloc_consistent() need a get_page() in the driver before I remap_page_range() it? Does memory allocated with __get_free_pages() need a get_page() in the driver before I remap_page_range() it?
And how about set_bit(PG_reserved, ...) on those pages? Is that something of the past?
#if 0 ... <vm_insert_page implementation here, disabled> ... #else /* remap_pfn_range */ #warning Using remap_pfn_range static int buffer_mmap(struct file *file, struct vm_area_struct *vma) { unsigned long vsize, vsize2; void *vaddr, *vaddr2; unsigned long start = vma->vm_start;
* VM_RESERVED: prevent the pages from being swapped out */ vma->vm_flags |= VM_RESERVED; vma->vm_private_data = file->private_data;
/* allocated using __get_free_pages() or pci_alloc_consistent() */ vaddr = buffer_virt; vsize = buffer_size;
/* iterate over pages */ vaddr2 = vaddr; vsize2 = vsize; while (vsize2 > 0) { printk(KERN_DEBUG "get_page(page=%p)\n", virt_to_page(vaddr2)); get_page(virt_to_page(vaddr2)); //set_bit(PG_reserved, &(virt_to_page(vaddr2)->flags)); vaddr2 += PAGE_SIZE; vsize2 -= PAGE_SIZE; } remap_pfn_range(vma, vma->vm_start, page_to_pfn(virt_to_page(vaddr)), vsize, vma->vm_page_prot); return 0; } #endif
Thanks for the explanation,
Regards, -- Leon
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