Why does power management corrupt SPI registers on STM32WLE5?

OK, here is what I have done, but use at your own risk, and this is unsupported!

First, the changes in PWR_EnterStopMode() and PWR_ExitStopMode():

void PWR_EnterStopMode(void)
{
	/* USER CODE BEGIN EnterStopMode_1 */
 
	// Save and restore SPI registers either side of STOP2 mode, since registers are not preserved
	if (boardUsesSPI()) {
		spiSaveState();
	}
 
	/* USER CODE END EnterStopMode_1 */
	/* Suspend sysTick : work around for degugger problem in dual core (tickets 71085, 72038, 71087 ) */
	HAL_SuspendTick();
	/* Clear Status Flag before entering STOP/STANDBY Mode */
	LL_PWR_ClearFlag_C1STOP_C1STB();
 
	/* USER CODE BEGIN EnterStopMode_2 */
 
	/* USER CODE END EnterStopMode_2 */
	HAL_PWREx_EnterSTOP2Mode(PWR_STOPENTRY_WFI);
	/* USER CODE BEGIN EnterStopMode_3 */
 
	/* USER CODE END EnterStopMode_3 */
}
 
void PWR_ExitStopMode(void)
{
	/* USER CODE BEGIN ExitStopMode_1 */
 
	/* USER CODE END ExitStopMode_1 */
	/* Resume sysTick : work around for degugger problem in dual core */
	HAL_ResumeTick();
	/*Not retained periph:
 ADC interface
 DAC interface USARTx, TIMx, i2Cx, SPIx
 SRAM ctrls, DMAx, DMAMux, AES, RNG, HSEM */
 
	/* Resume not retained USARTx and DMA */
	vcom_Resume();
	/* USER CODE BEGIN ExitStopMode_2 */
	// Save and restore SPI registers either side of STOP2 mode, since registers are not preserved
	if (boardUsesSPI()) {
		spiRestoreState();
	}
	/* USER CODE END ExitStopMode_2 */
}

Then spiSaveState() and spiRestoreState() are added to my own spi.c file:

// Save and restore SPI registers either side of STOP2 mode, since registers are not preserved
void spiSaveState(void) {
	HAL_SPI_Save_State(&hspi);
}
 
void spiRestoreState(void) {
	HAL_SPI_Restore_State(&hspi);
}

And these calls HAL_SPI_Save_State() and HAL_SPI_Restore_State() are added to stm32wlxx_hal_spi.c as follows:

// Save SPI registers either side of STOP2 mode, since registers are not preserved
void HAL_SPI_Save_State(SPI_HandleTypeDef *hspi) {
	hspi->saved_cr1 = READ_REG(hspi->Instance->CR1);
	hspi->saved_cr2 = READ_REG(hspi->Instance->CR2);
	// There are other r/w registers but not used by this app
}
 
// Restore SPI registers either side of STOP2 mode, since registers are not preserved
void HAL_SPI_Restore_State(SPI_HandleTypeDef *hspi) {
	WRITE_REG(hspi->Instance->CR1, hspi->saved_cr1);
	WRITE_REG(hspi->Instance->CR2, hspi->saved_cr2);
}

The variables that save the state (saved_cr1 and saved_cr2) are additions to the hspi structure, as follows:

typedef struct __SPI_HandleTypeDef
{
 SPI_TypeDef *Instance; /*!< SPI registers base address */
<snip>
 
 // Saved SPI register state here:
 uint32_t					saved_cr1;		// saved value of CR1
 uint32_t					saved_cr2;		// saved value of CR2
 
<snip>
} SPI_HandleTypeDef;

Obviously, I have only saved the state of registers that were causing me problems. This concept can be generalised to save whatever registers in whatever module you are using. This works well for me. Good luck.