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Blackfin arch: Add assembly function insl_16

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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>
This commit is contained in:
Michael Hennerich 2007-11-17 23:46:58 +08:00 committed by Bryan Wu
parent 1754a5d9f9
commit 5c91fb902d
3 changed files with 21 additions and 0 deletions
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1
arch/blackfin/kernel/bfin_ksyms.c
View file

@ -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);

19
arch/blackfin/lib/ins.S
View file

@ -77,3 +77,22 @@ ENTRY(_insb)
sti R3;
RTS;
ENDPROC(_insb)
ENTRY(_insl_16)
P0 = R0; /* P0 = port */
cli R3;
P1 = R1; /* P1 = address */
P2 = R2; /* P2 = count */
SSYNC;
LSETUP( .Llong16_loop_s, .Llong16_loop_e) LC0 = P2;
.Llong16_loop_s: R0 = [P0];
W[P1++] = R0;
R0 = R0 >> 16;
W[P1++] = R0;
NOP;
.Llong16_loop_e: NOP;
sti R3;
RTS;
ENDPROC(_insl_16)

1
include/asm-blackfin/io.h
View file

@ -122,6 +122,7 @@ extern void outsl(unsigned long port, const void *addr, unsigned long count);
extern void insb(unsigned long port, void *addr, unsigned long count);
extern void insw(unsigned long port, void *addr, unsigned long count);
extern void insl(unsigned long port, void *addr, unsigned long count);
extern void insl_16(unsigned long port, void *addr, unsigned long count);
extern void dma_outsb(unsigned long port, const void *addr, unsigned short count);
extern void dma_outsw(unsigned long port, const void *addr, unsigned short count);