1. The 2nd bootloader always call `rom_spiflash_unlock()`, but never help to clear the WEL bit when exit. This may cause system unstability.
This commit helps to clear WEL when flash configuration is done.
**RISK:** When the app starts, it didn't have to clear the WEL before it actually write/erase. But now the very first write/erase operation should be done after a WEL clear. Though the risk is little (all the following write/erase also need to clear the WEL), we still have to test this carefully, especially for those functions used by the OTA.
2. The `rom_spiflash_unlock()` function in the patch of ESP32 may (1) trigger the QPI, (2) clear the QE or (3) fail to unlock the ISSI chips.
Status register bitmap of ISSI chip and GD chip:
| SR | ISSI | GD25LQ32C |
| -- | ---- | --------- |
| 0 | WIP | WIP |
| 1 | WEL | WEL |
| 2 | BP0 | BP0 |
| 3 | BP1 | BP1 |
| 4 | BP2 | BP2 |
| 5 | BP3 | BP3 |
| 6 | QE | BP4 |
| 7 | SRWD | SRP0 |
| 8 | | SRP1 |
| 9 | | QE |
| 10 | | SUS2 |
| 11 | | LB1 |
| 12 | | LB2 |
| 13 | | LB3 |
| 14 | | CMP |
| 15 | | SUS1 |
QE bit of other chips are at the bit 9 of the status register (i.e. bit 1 of SR2), which should be read by RDSR2 command.
However, the RDSR2 (35H, Read Status 2) command for chip of other vendors happens to be the QIOEN (Enter QPI mode) command of ISSI chips. When the `rom_spiflash_unlock()` function trys to read SR2, it may trigger the QPI of ISSI chips.
Moreover, when `rom_spiflash_unlock()` try to clear the BP4 bit in the status register, QE (bit 6) of ISSI chip may be cleared by accident. Or if the ISSI chip doesn't accept WRSR command with argument of two bytes (since it only have status register of one byte), it may fail to clear the other protect bits (BP0~BP3) as expected.
This commit makes the `rom_spiflash_unlock()` check whether the vendor is issi. if so, `rom_spiflash_unlock()` only send RDSR to read the status register, send WRSR with only 1 byte argument, and also avoid clearing the QE bit (bit 6).
3. `rom_spiflash_unlock()` always send WRSR command to clear protection bits even when there is no protection bit active. And the execution of clearing status registers, which takes about 700us, will also happen even when there's no bits cleared.
This commit skips the clearing of status register if there is no protection bits active.
Also move the execute_flash_command to be a bootloader API; move
implementation of spi_flash_wrap_set to the bootloader
Goal is that multiple faults would be required to bypass a boot-time signature check.
- Also strengthens some address range checks for safe app memory addresses
- Change pre-enable logic to also check the bootloader signature before enabling SBV2 on ESP32
Add some additional checks for invalid sections:
- Sections only partially in DRAM or IRAM are invalid
- If a section is in D/IRAM, allow the possibility only some is in D/IRAM
- Only pass sections that are entirely in the same type of RTC memory region
Angus Gratton