[ot] hw/opentitan: ot_flash: clear erase suspend & documentation

This commit adds a "partway" fix for erase suspend implementation,
immediately clearing the request to simulate the response of "no erase
ongoing", as currently QEMU flash erases are modelled as synchronous
(i.e. the entire erase happens at once, and cannot be suspended).

Also updates the author information in the file prologue, and introduces
some additional documentation about the limitations of the current QEMU
model, and a couple of relevant TODOs.

Signed-off-by: Alex Jones <[email protected]>

Author: AlexJones0

hw/opentitan/ot_flash.c

@@ -6,6 +6,7 @@
  *
  * Author(s):
  *  Emmanuel Blot <[email protected]>
+ *  Alex Jones <[email protected]>
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -25,8 +26,15 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  *
- * Note: for now, only a minimalist subset of Power Manager device is
- *       implemented in order to enable OpenTitan's ROM boot to progress
+ * Known limitations:
+ *  - ECC/ICV/Scrambling functionality is not yet implemented in QEMU,
+ *    including ECC single error support.
+ *  - Alert functionality is not yet modelled (outside of test alerts).
+ *  - Program Repair / High Endurance enables are meaningless in the OpenTitan
+ *    Generic Flash Bank and so are not emulated.
+ *  - Erase Suspend is not emulated in QEMU (erases are done synchronously, so
+ *    you can suspend, but the bit will immediately be cleared).
+ *  - HW info cfg overrides are not modelled in QEMU.
  */
 
 #include "qemu/osdep.h"
@@ -769,6 +777,7 @@ static void ot_flash_update_irqs(OtFlashState *s)
 
 static void ot_flash_update_alerts(OtFlashState *s)
 {
+    /* @todo Implement non-test alert sources and update them here as well. */
     uint32_t level = s->regs[R_ALERT_TEST];
 
     for (unsigned ix = 0u; ix < PARAM_NUM_ALERTS; ix++) {
@@ -834,7 +843,6 @@ static void ot_flash_update_prog_watermark(OtFlashState *s)
     ot_flash_update_irqs(s);
 }
 
-
 static void ot_flash_op_signal(void *opaque)
 {
     OtFlashState *s = opaque;
@@ -1838,8 +1846,13 @@ static void ot_flash_regs_write(void *opaque, hwaddr addr, uint64_t val64,
         s->regs[reg] = val32;
         break;
     case R_ERASE_SUSPEND:
-        val32 &= R_ERASE_SUSPEND_REQ_MASK;
-        s->regs[reg] = val32;
+        /*
+         * @todo We do not implement the erase suspend operation in QEMU as we
+         * do all erases synchronously, and so just immediately clear the erase
+         * suspend request. To implement this feature properly we would have to
+         * add delay to bank erases & check for erase suspends at each step.
+         */
+        s->regs[reg] = 0u;
         break;
     case R_REGION_CFG_REGWEN_0:
     case R_REGION_CFG_REGWEN_1:
@@ -2498,6 +2511,8 @@ static void ot_flash_load(OtFlashState *s, Error **errp)
      *   - INFO1 bank 1
      *   - INFO2 bank 1
      * - Debug info (ELF file names)
+     *
+     * @todo Add ECC section to backend for ECC/ICV support also
      */
     flash->data = (uint32_t *)(base);
     flash->info =