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DMA prevents the system to suspend when an UART RX wake-up source is using DMA. DMA can't suspend while DMA channels are still active. Terminate DMA transfer at suspend, and restart a new DMA transfer at resume. Create stm32_usart_start_rx_dma_cyclic function to factorize dma RX initialization. Move RX DMA code related to wakeup into stm32_usart_serial_en_wakeup() routine to ease further improvements on wakeup from low power modes. Don't enable/disable wakeup on uninitialized port. There may be data residue in the RX FIFO while suspending. Flush it at suspend time. Receiver timeout interrupt won't trigger later in low power mode, so call stm32_usart_receive_chars() in case there's data to handle. Signed-off-by: Valentin Caron <valentin.caron@foss.st.com> Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com> Link: https://lore.kernel.org/r/20211025134229.8456-3-erwan.leray@foss.st.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.