[Qemu-devel] [PATCH 4/7] opencores_eth: fix RX path: FCS, padding and TL

[Max Filippov <jcmvbkbc@gmail.com>]

OpenCores 10/100 Mbps Ethernet MAC specification doesn't clearly state
whether FCS is counted in the RX frame length or not. Looks like it is.
Append zero FCS to the received frames.

Get rid of big static buffer for RX frame padding, optimize it for the
most common MINFL value range.

Set RXD_TL for the long frames only when HUGEN bit is set.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
 hw/opencores_eth.c |   29 ++++++++++++++++++++++++-----
 1 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/hw/opencores_eth.c b/hw/opencores_eth.c
index 64b616e..2c1e475 100644
--- a/hw/opencores_eth.c
+++ b/hw/opencores_eth.c
@@ -382,6 +382,7 @@ static ssize_t open_eth_receive(VLANClientState *nc,
     OpenEthState *s = DO_UPCAST(NICState, nc, nc)->opaque;
     size_t maxfl = GET_REGFIELD(s, PACKETLEN, MAXFL);
     size_t minfl = GET_REGFIELD(s, PACKETLEN, MINFL);
+    size_t fcsl = 4;
     bool miss = true;
 
     trace_open_eth_receive((unsigned)size);
@@ -418,6 +419,7 @@ static ssize_t open_eth_receive(VLANClientState *nc,
 #else
     {
 #endif
+        static const uint8_t zero[64] = {0};
         desc *desc = rx_desc(s);
         size_t copy_size = GET_REGBIT(s, MODER, HUGEN) ? 65536 : maxfl;
 
@@ -426,11 +428,13 @@ static ssize_t open_eth_receive(VLANClientState *nc,
 
         if (copy_size > size) {
             copy_size = size;
+        } else {
+            fcsl = 0;
         }
         if (miss) {
             desc->len_flags |= RXD_M;
         }
-        if (size > maxfl) {
+        if (GET_REGBIT(s, MODER, HUGEN) && size > maxfl) {
             desc->len_flags |= RXD_TL;
         }
 #ifdef USE_RECSMALL
@@ -442,13 +446,28 @@ static ssize_t open_eth_receive(VLANClientState *nc,
         cpu_physical_memory_write(desc->buf_ptr, buf, copy_size);
 
         if (GET_REGBIT(s, MODER, PAD) && copy_size < minfl) {
-            static const uint8_t zero[65536] = {0};
+            if (minfl - copy_size > fcsl) {
+                fcsl = 0;
+            } else {
+                fcsl -= minfl - copy_size;
+            }
+            while (copy_size < minfl) {
+                size_t zero_sz = minfl - copy_size < sizeof(zero) ?
+                    minfl - copy_size : sizeof(zero);
 
-            cpu_physical_memory_write(desc->buf_ptr + copy_size,
-                    zero, minfl - copy_size);
-            copy_size = minfl;
+                cpu_physical_memory_write(desc->buf_ptr + copy_size,
+                        zero, zero_sz);
+                copy_size += zero_sz;
+            }
         }
 
+        /* There's no FCS in the frames handed to us by the QEMU, zero fill it.
+         * Don't do it if the frame is cut at the MAXFL or padded with 4 or
+         * more bytes to the MINFL.
+         */
+        cpu_physical_memory_write(desc->buf_ptr + copy_size, zero, fcsl);
+        copy_size += fcsl;
+
         SET_FIELD(desc->len_flags, RXD_LEN, copy_size);
 
         if ((desc->len_flags & RXD_WRAP) || s->rx_desc == 0x7f) {
-- 
1.7.6.4