driver: flash: enable stm32 read-back protection at runtime #91945
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do not force option byte reloading in the write function because RDP byte cannot be reloaded that way: it needs a POR through Standby mode. when FLASH_CR_OBL_LAUNCH is defined, use it to force-reload option bytes directly in the locking function. Signed-off-by: Cyril Fougeray <[email protected]>
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for the read-back protection option byte to be successfully reloaded at runtime, a power-on reset can be achieved by putting the microcontroller into Standby mode and waking up from that mode. Signed-off-by: Cyril Fougeray <[email protected]>
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| /* enter SLEEP mode : WFE or WFI */ | ||
| k_cpu_idle(); |
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| /* enter SLEEP mode : WFE or WFI */ | |
| k_cpu_idle(); | |
| __disable_irq(); | |
| __SEV(); | |
| __WFE(); | |
| __WFE(); |
otherwise entry in low-power state is not guaranteed (and even this sequence may not be 100% safe)
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I think we should have a STM32 SoC helper function to go into Standby mode.
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This should go in common flash code if anywhere; PM needs something else (we don't want to force entry in low-power mode while doing PM, unlike here)
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Note that is function should never return unless it fails (to reach SoC standby mode). I think the function declaration inline description should reflect this.
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True too, I guess it should be FUNC_NORETURN + end with an infinite loop
drivers/flash/flash_stm32l4x.c
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| #include <stm32_ll_system.h> | ||
| #include <stm32l4xx_ll_cortex.h> | ||
| #include <stm32l4xx_ll_pwr.h> |
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Why adding these header files?
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| /* Force the option byte loading */ | ||
| regs->CR |= FLASH_CR_OBL_LAUNCH; |
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Option bytes other than RDP in OTPR require OBL_LAUNCH or power reset to be loaded.
I think setting here OBL_LAUNCH is still applicable while flash_stm32_set_rdp_level() can still force a power reset (as proposed in next commit).
| /* Force the option byte loading before locking */ | ||
| if (enable) { | ||
| regs->CR |= FLASH_CR_OBL_LAUNCH; | ||
| } |
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I think this change makes sense but would deserve a dedicated commit, aside proposing changes in flash_stm32_option_bytes_write().
| /* enter SLEEP mode : WFE or WFI */ | ||
| k_cpu_idle(); |
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I think we should have a STM32 SoC helper function to go into Standby mode.
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@fouge Do you plan to push this PR further ? |
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when writing the read-back protection option byte, the stm32 target must go through a power-on reset to reload the option bytes correctly, which is achieved by going into Standby or Shutdown mode.
using the OBL bit locks the microcontroller in a bad state waiting for a full power cycle, this buggy behavior has been added in that PR.
Instead of force-reloading when writing any option byte, it's now performed when re-locking the option bytes, and if OBL bit is defined. Locking doesn't apply when changing the RDP level, since it goes through a POR, so this solution allows to set and reload any option byte correctly.
see extract from stm32g4xx datasheet:
a few concerns: