net/cadence_gem: Fix register w1c logic

This write-1-clear logic was incorrect. It was always clearing w1c
bits regardless of whether the written value was 1 or not. i.e. it
was implementing a write-anything-to-clear strategy.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: ed905b04d3343966ded425f06aa2224bc7a35b59.1386136219.git.peter.crosthwaite@xilinx.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 6 insertions, 7 deletions

diff --git a/hw/net/cadence_gem.c b/hw/net/cadence_gem.c
index 1619507e55..f2c734ef2b 100644
--- a/hw/net/cadence_gem.c
+++ b/hw/net/cadence_gem.c
@@ -1112,15 +1112,14 @@ static void gem_write(void *opaque, hwaddr offset, uint64_t val,
 
     /* Squash bits which are read only in write value */
     val &= ~(s->regs_ro[offset]);
-    /* Preserve (only) bits which are read only in register */
-    readonly = s->regs[offset];
-    readonly &= s->regs_ro[offset];
-
-    /* Squash bits which are write 1 to clear */
-    val &= ~(s->regs_w1c[offset] & val);
+    /* Preserve (only) bits which are read only and wtc in register */
+    readonly = s->regs[offset] & (s->regs_ro[offset] | s->regs_w1c[offset]);
 
     /* Copy register write to backing store */
-    s->regs[offset] = val | readonly;
+    s->regs[offset] = (val & ~s->regs_w1c[offset]) | readonly;
+
+    /* do w1c */
+    s->regs[offset] &= ~(s->regs_w1c[offset] & val);
 
     /* Handle register write side effects */
     switch (offset) {