[PATCH v4 14/21] hw/block/m25p80: Implement volatile status register write enable for Winbond

[Jamin Lin <jamin_lin@aspeedtech.com>]

Winbond SPI NOR flashes require the Volatile Status Register Write Enable
(VSR WREN, opcode 0x50) command to be issued before updating volatile
status register bits, such as those accessed via the WRSR2 command.

Currently, WRSR2 handling only checks the standard write enable latch,
which does not fully model Winbond hardware behavior.

Add support for the volatile write enable mechanism by introducing a
separate volatile_write_enable flag. For Winbond devices, WRSR2 writes
that update volatile status register bits are gated by the VSR WREN
command. If the volatile write enable latch is not set, such writes are
rejected.

Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
---
 hw/block/m25p80.c | 36 ++++++++++++++++++++++++++++++++----
 1 file changed, 32 insertions(+), 4 deletions(-)

diff --git a/hw/block/m25p80.c b/hw/block/m25p80.c
index b8a2543c0b..5bb8b8efa9 100644
--- a/hw/block/m25p80.c
+++ b/hw/block/m25p80.c
@@ -438,6 +438,11 @@ typedef enum {
      */
     WRSR2 = 0x31,
 
+    /*
+     * Winbond: 0x50 - Write Enable for Volatile Status Register
+     */
+    VSR_WREN = 0x50,
+
     RNVCR = 0xB5,
     WNVCR = 0xB1,
 
@@ -510,6 +515,7 @@ struct Flash {
     uint8_t spansion_cr4v;
     bool wp_level;
     bool write_enable;
+    bool volatile_write_enable;
     bool four_bytes_address_mode;
     bool reset_enable;
     bool quad_enable;
@@ -897,6 +903,7 @@ static void reset_memory(Flash *s)
     s->pos = 0;
     s->state = STATE_IDLE;
     s->write_enable = false;
+    s->volatile_write_enable = false;
     s->reset_enable = false;
     s->quad_enable = false;
     s->aai_enable = false;
@@ -1305,8 +1312,7 @@ static void decode_new_cmd(Flash *s, uint32_t value)
          * combinations of the two states are called "software protected mode"
          * (SPM), and status register writes are permitted.
          */
-        if ((s->wp_level == 0 && s->status_register_write_disabled)
-            || !s->write_enable) {
+        if (s->wp_level == 0 && s->status_register_write_disabled) {
             qemu_log_mask(LOG_GUEST_ERROR,
                           "M25P80: Status register 2 write is disabled!\n");
             break;
@@ -1314,6 +1320,17 @@ static void decode_new_cmd(Flash *s, uint32_t value)
 
         switch (get_man(s)) {
         case MAN_WINBOND:
+            /*
+             * Winbond requires VSR WREN (0x50) prior to updating volatile
+             * status register bits. VSR WREN does not set WEL.
+             *
+             * Accept either standard WEL (0x06) or VSR WREN (0x50).
+             */
+            if (!s->write_enable && !s->volatile_write_enable) {
+                qemu_log_mask(LOG_GUEST_ERROR,
+                              "M25P80: Status register 2 write is disabled!\n");
+                break;
+            }
             s->needed_bytes = 1;
             s->state = STATE_COLLECTING_DATA;
             s->pos = 0;
@@ -1332,6 +1349,16 @@ static void decode_new_cmd(Flash *s, uint32_t value)
         s->write_enable = true;
         break;
 
+    case VSR_WREN:
+        switch (get_man(s)) {
+        case MAN_WINBOND:
+            s->volatile_write_enable = true;
+            break;
+        default:
+            break;
+        }
+        break;
+
     case RDSR:
         s->data[0] = (!!s->write_enable) << 1;
         s->data[0] |= (!!s->status_register_write_disabled) << 7;
@@ -1824,8 +1851,8 @@ static const VMStateDescription vmstate_m25p80_block_protect = {
 
 static const VMStateDescription vmstate_m25p80 = {
     .name = "m25p80",
-    .version_id = 0,
-    .minimum_version_id = 0,
+    .version_id = 1,
+    .minimum_version_id = 1,
     .pre_save = m25p80_pre_save,
     .pre_load = m25p80_pre_load,
     .fields = (const VMStateField[]) {
@@ -1837,6 +1864,7 @@ static const VMStateDescription vmstate_m25p80 = {
         VMSTATE_UINT8(cmd_in_progress, Flash),
         VMSTATE_UINT32(cur_addr, Flash),
         VMSTATE_BOOL(write_enable, Flash),
+        VMSTATE_BOOL(volatile_write_enable, Flash),
         VMSTATE_BOOL(reset_enable, Flash),
         VMSTATE_UINT8(ear, Flash),
         VMSTATE_BOOL(four_bytes_address_mode, Flash),
-- 
2.43.0