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>

2 files changed, 20 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);
diff --git a/arch/blackfin/lib/ins.S b/arch/blackfin/lib/ins.S
index a17cc77ac36f..df7b8833a0c5 100644
--- a/arch/blackfin/lib/ins.S
+++ b/arch/blackfin/lib/ins.S
@@ -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)