portio_list_add_1() creates a MemoryRegionPortioList instance which holds a
MemoryRegion `mr` and an array of MemoryRegionPortio elements named `ports`.
Each element in the array gets assigned the same value for its .base attribute.
The same value also ends up as the .addr attribute of `mr` due to the
memory_region_add_subregion() call. This means that all .base attributes are
the same as `mr.addr`.

The only usages of MemoryRegionPortio::base were in portio_read() and
portio_write(). Both functions get above MemoryRegionPortioList as their
opaque parameter. In both cases find_portio() can only return one of the
MemoryRegionPortio elements of the `ports` array. Due to above observation any
element will have the same .base value equal to `mr.addr` which is also
accessible.

Hence, `mrpio->mr.addr` is equivalent to `mrp->base` and
MemoryRegionPortio::base is redundant and can be removed.

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
---
 include/exec/ioport.h |  1 -
 system/ioport.c       | 13 ++++++-------
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/include/exec/ioport.h b/include/exec/ioport.h
index e34f668998..95f1dc30d0 100644
--- a/include/exec/ioport.h
+++ b/include/exec/ioport.h
@@ -35,7 +35,6 @@ typedef struct MemoryRegionPortio {
     unsigned size;
     uint32_t (*read)(void *opaque, uint32_t address);
     void (*write)(void *opaque, uint32_t address, uint32_t data);
-    uint32_t base; /* private field */
 } MemoryRegionPortio;
 
 #define PORTIO_END_OF_LIST() { }
diff --git a/system/ioport.c b/system/ioport.c
index 1824aa808c..a59e58b716 100644
--- a/system/ioport.c
+++ b/system/ioport.c
@@ -181,13 +181,13 @@ static uint64_t portio_read(void *opaque, hwaddr addr, unsigned size)
 
     data = ((uint64_t)1 << (size * 8)) - 1;
     if (mrp) {
-        data = mrp->read(mrpio->portio_opaque, mrp->base + addr);
+        data = mrp->read(mrpio->portio_opaque, mrpio->mr.addr + addr);
     } else if (size == 2) {
         mrp = find_portio(mrpio, addr, 1, false);
         if (mrp) {
-            data = mrp->read(mrpio->portio_opaque, mrp->base + addr);
+            data = mrp->read(mrpio->portio_opaque, mrpio->mr.addr + addr);
             if (addr + 1 < mrp->offset + mrp->len) {
-                data |= mrp->read(mrpio->portio_opaque, mrp->base + addr + 1) << 8;
+                data |= mrp->read(mrpio->portio_opaque, mrpio->mr.addr + addr + 1) << 8;
             } else {
                 data |= 0xff00;
             }
@@ -203,13 +203,13 @@ static void portio_write(void *opaque, hwaddr addr, uint64_t data,
     const MemoryRegionPortio *mrp = find_portio(mrpio, addr, size, true);
 
     if (mrp) {
-        mrp->write(mrpio->portio_opaque, mrp->base + addr, data);
+        mrp->write(mrpio->portio_opaque, mrpio->mr.addr + addr, data);
     } else if (size == 2) {
         mrp = find_portio(mrpio, addr, 1, true);
         if (mrp) {
-            mrp->write(mrpio->portio_opaque, mrp->base + addr, data & 0xff);
+            mrp->write(mrpio->portio_opaque, mrpio->mr.addr + addr, data & 0xff);
             if (addr + 1 < mrp->offset + mrp->len) {
-                mrp->write(mrpio->portio_opaque, mrp->base + addr + 1, data >> 8);
+                mrp->write(mrpio->portio_opaque, mrpio->mr.addr + addr + 1, data >> 8);
             }
         }
     }
@@ -244,7 +244,6 @@ static void portio_list_add_1(PortioList *piolist,
     /* Adjust the offsets to all be zero-based for the region.  */
     for (i = 0; i < count; ++i) {
         mrpio->ports[i].offset -= off_low;
-        mrpio->ports[i].base = start + off_low;
     }
 
     /*
-- 
2.43.0