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authorMichael Hennerich <michael.hennerich@analog.com>2007-11-17 23:46:58 +0800
committerBryan Wu <bryan.wu@analog.com>2007-11-17 23:46:58 +0800
commit5c91fb902d4e6f6006faf45edd3f25932cb7d58c (patch)
tree0bdf4457456a6bc8f794078e22a885dc44b2d159 /arch/blackfin/kernel
parentBlackfin arch: use do_div() for the 64bit division as pointed out by Bernd (diff)
downloadlinux-dev-5c91fb902d4e6f6006faf45edd3f25932cb7d58c.tar.xz
linux-dev-5c91fb902d4e6f6006faf45edd3f25932cb7d58c.zip
Blackfin arch: Add assembly function insl_16
/* * CPUs often take a performance hit when accessing unaligned memory * locations. The actual performance hit varies, it can be small if the * hardware handles it or large if we have to take an exception and fix * it * in software. * * Since an ethernet header is 14 bytes network drivers often end up * with * the IP header at an unaligned offset. The IP header can be aligned by * shifting the start of the packet by 2 bytes. Drivers should do this * with: * * skb_reserve(NET_IP_ALIGN); * * The downside to this alignment of the IP header is that the DMA is * now * unaligned. On some architectures the cost of an unaligned DMA is high * and this cost outweighs the gains made by aligning the IP header. * * Since this trade off varies between architectures, we allow * NET_IP_ALIGN * to be overridden. */ This new function insl_16 allows to read form 32-bit IO and writes to 16-bit aligned memory. This is useful in above described scenario - In particular with the AXIS AX88180 Gigabit Ethernet MAC. Once the device is in 32-bit mode, reads from the RX FIFO always decrements 4bytes. While on the other side the destination address in SDRAM is always 16-bit aligned. If we use skb_reserve(0) the receive buffer is 32-bit aligned but later we hit a unaligned exception in the IP code. Signed-off-by: Michael Hennerich <michael.hennerich@analog.com> Signed-off-by: Bryan Wu <bryan.wu@analog.com>
Diffstat (limited to '')
-rw-r--r--arch/blackfin/kernel/bfin_ksyms.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/blackfin/kernel/bfin_ksyms.c b/arch/blackfin/kernel/bfin_ksyms.c
index 5dad9d380952..b3fa7d8fde6a 100644
--- a/arch/blackfin/kernel/bfin_ksyms.c
+++ b/arch/blackfin/kernel/bfin_ksyms.c
@@ -100,6 +100,7 @@ EXPORT_SYMBOL(outsw);
EXPORT_SYMBOL(insw);
EXPORT_SYMBOL(outsl);
EXPORT_SYMBOL(insl);
+EXPORT_SYMBOL(insl_16);
EXPORT_SYMBOL(irq_flags);
EXPORT_SYMBOL(iounmap);
EXPORT_SYMBOL(blackfin_dcache_invalidate_range);