Messages in this thread |  | | Date | Tue, 8 Jan 2013 09:24:22 -0700 | From | Jonathan Corbet <> | Subject | Re: 2nd attempt: help with dma_alloc_coherent() + dma_free_coherent() |
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On Tue, 8 Jan 2013 23:51:59 +0800 Jeff Chua <jeff.chua.linux@gmail.com> wrote:
> I'm trying to understand how this oops in the diva driver and it's just a > simple dma_alloc_coherent() followed by dma_free_coherent(), but it oops. > Why?
Hmm...from a quick look...
> static u32 *clock_data_addr; > static dma_addr_t clock_data_bus_addr; > > if((clock_data_addr = dma_alloc_coherent(NULL, PAGE_SIZE, > &clock_data_bus_addr, GFP_KERNEL)) != 0) { > printk(KERN_INFO "dma_alloc_coherent ok\n"); > memset (clock_data_addr, 0x00, PAGE_SIZE); > } else > printk(KERN_INFO "dma_alloc_coherent bad!!!\n"); > if(clock_data_addr) { > printk(KERN_INFO "dma_free_coherent!!!\n"); > dma_free_coherent(NULL, PAGE_SIZE, clock_data_addr, > clock_data_bus_addr); > clock_data_addr = NULL; > }
Perhaps passing NULL as your device structure pointer might just have something to do with a crash due to a null pointer dereference? If you're doing DMA, you should have a device. Try passing it and you might just find that things work better.
(Incidentally, this:
> IP: [<ffffffff813ec01c>] iommu_no_mapping+0xc/0xee
is a fairly good clue as well - it's trying to dereference the device structure pointer).
jon
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