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/* * 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> |
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| .. | ||
| asm-offsets.c | ||
| bfin_dma_5xx.c | ||
| bfin_gpio.c | ||
| bfin_ksyms.c | ||
| cacheinit.c | ||
| cplbinit.c | ||
| dma-mapping.c | ||
| dualcore_test.c | ||
| early_printk.c | ||
| entry.S | ||
| fixed_code.S | ||
| flat.c | ||
| gptimers.c | ||
| init_task.c | ||
| irqchip.c | ||
| kgdb.c | ||
| Makefile | ||
| module.c | ||
| process.c | ||
| ptrace.c | ||
| reboot.c | ||
| setup.c | ||
| signal.c | ||
| sys_bfin.c | ||
| time.c | ||
| traps.c | ||
| vmlinux.lds.S | ||