How to configure UART after wake up?

I am working with STM32L152VD. After waking up from sleep and switching to 8Mhz. everything work properly (SPI,I2C,..) except UART.
I configure it using following function:

void uart1_configuration(void)
{
  USART_InitTypeDef USART_InitStructure;
  GPIO_InitTypeDef GPIO_InitStructure;

  RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1,ENABLE);

  GPIO_PinAFConfig(GPIOA, GPIO_PinSource9, GPIO_AF_USART1);
  GPIO_PinAFConfig(GPIOA, GPIO_PinSource10, GPIO_AF_USART1);

  /* Configure USART2 pins:  Rx and Tx ----------------------------*/
  GPIO_InitStructure.GPIO_Pin =  GPIO_Pin_9 | GPIO_Pin_10;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_2MHz;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;
  GPIO_Init(GPIOA, &GPIO_InitStructure);

  USART_InitStructure.USART_BaudRate = 9600;
  USART_InitStructure.USART_WordLength = USART_WordLength_8b;
  USART_InitStructure.USART_StopBits = USART_StopBits_1;
  USART_InitStructure.USART_Parity = USART_Parity_No;
  USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
  USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
  USART_Init(USART1, &USART_InitStructure);

  USART_Cmd(USART1,ENABLE);
        /* Enable RXNE interrupt */
  USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);
    /* Enable USART1 global interrupt */
  NVIC_EnableIRQ(USART1_IRQn);

}

It Seems UART is disabled.