Messages in this thread | | | From | John Keller <> | Subject | Re: [PATCH] ia64: SN specific version of dma_get_required_mask() | Date | Tue, 18 Nov 2008 09:53:04 -0600 (CST) |
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> > > This patch addresses a problem on SN Altix systems with < 4GB, where > > device drivers using the dma_get_required_mask() API would be told > > to use 32 bit DMA, when 64 bit is more efficient. > > Even if someone did configure an Altix with < 4GB (which seems a very > unlikely occurance) all of that 4G would be located above 4GB (lowest > physical address on Altix is something like 384 TB, isn't it?) > > Did we really make some dma mask decisions based on the amount > of memory rather than its location? If we do, then perhaps we > should fix this in a generic place, not in sn2 specific code. > > -Tony >
This is the generic routine for all archs and platforms...
drivers/base/platform.c
#ifndef ARCH_HAS_DMA_GET_REQUIRED_MASK u64 dma_get_required_mask(struct device *dev) { u32 low_totalram = ((max_pfn - 1) << PAGE_SHIFT); u32 high_totalram = ((max_pfn - 1) >> (32 - PAGE_SHIFT)); u64 mask;
if (!high_totalram) { /* convert to mask just covering totalram */ low_totalram = (1 << (fls(low_totalram) - 1)); low_totalram += low_totalram - 1; mask = low_totalram; } else { high_totalram = (1 << (fls(high_totalram) - 1)); high_totalram += high_totalram - 1; mask = (((u64)high_totalram) << 32) + 0xffffffff; } return mask; } EXPORT_SYMBOL_GPL(dma_get_required_mask); #endif
John ----
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