de2104x: support for systems lacking cache coherence

Add a configurable Descriptor Skip Length for systems that lack cache
coherence.

(akpm: I think this should be done as a module parameter, not a
compile-tinme option)

Signed-off-by: Risto Suominen <Risto.Suominen@gmail.com>
Cc: Grant Grundler <grundler@parisc-linux.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 24 insertions, 1 deletions

diff --git a/drivers/net/tulip/Kconfig b/drivers/net/tulip/Kconfig
index d913405bc393..1cc8cf4425d1 100644
--- a/drivers/net/tulip/Kconfig
+++ b/drivers/net/tulip/Kconfig
@@ -27,6 +27,18 @@ config DE2104X
           To compile this driver as a module, choose M here. The module will
           be called de2104x.
 
+config DE2104X_DSL
+        int "Descriptor Skip Length in 32 bit longwords"
+        depends on DE2104X
+        range 0 31
+        default 0
+        help
+          Setting this value allows to align ring buffer descriptors into their
+          own cache lines. Value of 4 corresponds to the typical 32 byte line
+          (the descriptor is 16 bytes). This is necessary on systems that lack
+          cache coherence, an example is PowerMac 5500. Otherwise 0 is safe.
+          Default is 0, and range is 0 to 31.
+
 config TULIP
         tristate "DECchip Tulip (dc2114x) PCI support"
         depends on PCI
diff --git a/drivers/net/tulip/de2104x.c b/drivers/net/tulip/de2104x.c
index d4c5ecc51f77..e7609a05032d 100644
--- a/drivers/net/tulip/de2104x.c
+++ b/drivers/net/tulip/de2104x.c
@@ -82,6 +82,13 @@ MODULE_PARM_DESC (rx_copybreak, "de2104x Breakpoint at which Rx packets are copi
                                  NETIF_MSG_RX_ERR       | \
                                  NETIF_MSG_TX_ERR)
 
+/* Descriptor skip length in 32 bit longwords. */
+#ifndef CONFIG_DE2104X_DSL
+#define DSL                     0
+#else
+#define DSL                     CONFIG_DE2104X_DSL
+#endif
+
 #define DE_RX_RING_SIZE         64
 #define DE_TX_RING_SIZE         64
 #define DE_RING_BYTES           \
@@ -153,6 +160,7 @@ enum {
         CmdReset                = (1 << 0),
         CacheAlign16            = 0x00008000,
         BurstLen4               = 0x00000400,
+        DescSkipLen             = (DSL << 2),
 
         /* Rx/TxPoll bits */
         NormalTxPoll            = (1 << 0),
@@ -246,7 +254,7 @@ static const u32 de_intr_mask =
  * Set the programmable burst length to 4 longwords for all:
  * DMA errors result without these values. Cache align 16 long.
  */
-static const u32 de_bus_mode = CacheAlign16 | BurstLen4;
+static const u32 de_bus_mode = CacheAlign16 | BurstLen4 | DescSkipLen;
 
 struct de_srom_media_block {
         u8                      opts;
@@ -266,6 +274,9 @@ struct de_desc {
         __le32                  opts2;
         __le32                  addr1;
         __le32                  addr2;
+#if DSL
+        __le32                  skip[DSL];
+#endif
 };
 
 struct media_info {