net: ethernet: pcnet32: Setup the SRAM and NOUFLO on Am79C97{3, 5}

On a MIPS Malta board, tons of fifo underflow errors have been observed
when using u-boot as bootloader instead of YAMON. The reason for that
is that YAMON used to set the pcnet device to SRAM mode but u-boot does
not. As a result, the default Tx threshold (64 bytes) is now too small to
keep the fifo relatively used and it can result to Tx fifo underflow errors.
As a result of which, it's best to setup the SRAM on supported controllers
so we can always use the NOUFLO bit.

Cc: <netdev@vger.kernel.org>
Cc: <stable@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>
Cc: Don Fry <pcnet32@frontier.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 29 insertions, 2 deletions

diff --git a/drivers/net/ethernet/amd/pcnet32.c b/drivers/net/ethernet/amd/pcnet32.c
index 11d6e6561df1..15a8190a6f75 100644
--- a/drivers/net/ethernet/amd/pcnet32.c
+++ b/drivers/net/ethernet/amd/pcnet32.c
@@ -1543,7 +1543,7 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
 {
         struct pcnet32_private *lp;
         int i, media;
-        int fdx, mii, fset, dxsuflo;
+        int fdx, mii, fset, dxsuflo, sram;
         int chip_version;
         char *chipname;
         struct net_device *dev;
@@ -1580,7 +1580,7 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
         }
 
         /* initialize variables */
-        fdx = mii = fset = dxsuflo = 0;
+        fdx = mii = fset = dxsuflo = sram = 0;
         chip_version = (chip_version >> 12) & 0xffff;
 
         switch (chip_version) {
@@ -1613,6 +1613,7 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
                 chipname = "PCnet/FAST III 79C973";     /* PCI */
                 fdx = 1;
                 mii = 1;
+                sram = 1;
                 break;
         case 0x2626:
                 chipname = "PCnet/Home 79C978"; /* PCI */
@@ -1636,6 +1637,7 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
                 chipname = "PCnet/FAST III 79C975";     /* PCI */
                 fdx = 1;
                 mii = 1;
+                sram = 1;
                 break;
         case 0x2628:
                 chipname = "PCnet/PRO 79C976";
@@ -1664,6 +1666,31 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
                 dxsuflo = 1;
         }
 
+        /*
+         * The Am79C973/Am79C975 controllers come with 12K of SRAM
+         * which we can use for the Tx/Rx buffers but most importantly,
+         * the use of SRAM allow us to use the BCR18:NOUFLO bit to avoid
+         * Tx fifo underflows.
+         */
+        if (sram) {
+                /*
+                 * The SRAM is being configured in two steps. First we
+                 * set the SRAM size in the BCR25:SRAM_SIZE bits. According
+                 * to the datasheet, each bit corresponds to a 512-byte
+                 * page so we can have at most 24 pages. The SRAM_SIZE
+                 * holds the value of the upper 8 bits of the 16-bit SRAM size.
+                 * The low 8-bits start at 0x00 and end at 0xff. So the
+                 * address range is from 0x0000 up to 0x17ff. Therefore,
+                 * the SRAM_SIZE is set to 0x17. The next step is to set
+                 * the BCR26:SRAM_BND midway through so the Tx and Rx
+                 * buffers can share the SRAM equally.
+                 */
+                a->write_bcr(ioaddr, 25, 0x17);
+                a->write_bcr(ioaddr, 26, 0xc);
+                /* And finally enable the NOUFLO bit */
+                a->write_bcr(ioaddr, 18, a->read_bcr(ioaddr, 18) | (1 << 11));
+        }
+
         dev = alloc_etherdev(sizeof(*lp));
         if (!dev) {
                 ret = -ENOMEM;