[Qemu-devel] [PATCH v2 4/4] fw_cfg: streamline (non-DMA) read operations

["Gabriel L. Somlo" <somlo@cmu.edu>]

Replace fw_cfg_comb_read(), fw_cfg_data_mem_read(), and fw_cfg_read()
with a single method, fw_cfg_data_read(), which works on all possible
read sizes (single- or multi-byte). The new method also eliminates
redundant validity checks caused by multi-byte reads repeatedly invoking
the old single-byte fw_cfg_read() method.

Also update trace_fw_cfg_read() prototype to accept a 64-bit value
argument.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Marc Marí <markmb@redhat.com>
Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
---
 hw/nvram/fw_cfg.c | 37 ++++++++++---------------------------
 trace-events      |  2 +-
 2 files changed, 11 insertions(+), 28 deletions(-)

diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index 5de6dbc..cd477f9 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -274,32 +274,20 @@ static int fw_cfg_select(FWCfgState *s, uint16_t key)
     return ret;
 }
 
-static uint8_t fw_cfg_read(FWCfgState *s)
+static uint64_t fw_cfg_data_read(void *opaque, hwaddr addr, unsigned size)
 {
+    FWCfgState *s = opaque;
     int arch = !!(s->cur_entry & FW_CFG_ARCH_LOCAL);
     FWCfgEntry *e = &s->entries[arch][s->cur_entry & FW_CFG_ENTRY_MASK];
-    uint8_t ret;
-
-    if (s->cur_entry == FW_CFG_INVALID || !e->data || s->cur_offset >= e->len)
-        ret = 0;
-    else {
-        ret = e->data[s->cur_offset++];
-    }
-
-    trace_fw_cfg_read(s, ret);
-    return ret;
-}
-
-static uint64_t fw_cfg_data_mem_read(void *opaque, hwaddr addr,
-                                     unsigned size)
-{
-    FWCfgState *s = opaque;
     uint64_t value = 0;
-    unsigned i;
 
-    for (i = 0; i < size; ++i) {
-        value = (value << 8) | fw_cfg_read(s);
+    if (s->cur_entry != FW_CFG_INVALID && e->data) {
+        while (size-- && s->cur_offset < e->len) {
+            value = (value << 8) | e->data[s->cur_offset++];
+        }
     }
+
+    trace_fw_cfg_read(s, value);
     return value;
 }
 
@@ -451,11 +439,6 @@ static bool fw_cfg_ctl_mem_valid(void *opaque, hwaddr addr,
     return is_write && size == 2;
 }
 
-static uint64_t fw_cfg_comb_read(void *opaque, hwaddr addr,
-                                 unsigned size)
-{
-    return fw_cfg_read(opaque);
-}
 
 static void fw_cfg_comb_write(void *opaque, hwaddr addr,
                               uint64_t value, unsigned size)
@@ -483,7 +466,7 @@ static const MemoryRegionOps fw_cfg_ctl_mem_ops = {
 };
 
 static const MemoryRegionOps fw_cfg_data_mem_ops = {
-    .read = fw_cfg_data_mem_read,
+    .read = fw_cfg_data_read,
     .write = fw_cfg_data_mem_write,
     .endianness = DEVICE_BIG_ENDIAN,
     .valid = {
@@ -494,7 +477,7 @@ static const MemoryRegionOps fw_cfg_data_mem_ops = {
 };
 
 static const MemoryRegionOps fw_cfg_comb_mem_ops = {
-    .read = fw_cfg_comb_read,
+    .read = fw_cfg_data_read,
     .write = fw_cfg_comb_write,
     .endianness = DEVICE_LITTLE_ENDIAN,
     .valid.accepts = fw_cfg_comb_valid,
diff --git a/trace-events b/trace-events
index bdfe79f..a0eb1d8 100644
--- a/trace-events
+++ b/trace-events
@@ -196,7 +196,7 @@ ecc_diag_mem_readb(uint64_t addr, uint32_t ret) "Read diagnostic %"PRId64"= %02x
 
 # hw/nvram/fw_cfg.c
 fw_cfg_select(void *s, uint16_t key, int ret) "%p key %d = %d"
-fw_cfg_read(void *s, uint8_t ret) "%p = %d"
+fw_cfg_read(void *s, uint64_t ret) "%p = %"PRIx64
 fw_cfg_add_file(void *s, int index, char *name, size_t len) "%p #%d: %s (%zd bytes)"
 
 # hw/block/hd-geometry.c
-- 
2.4.3