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Data may be stored in DMA RX buffer, when suspending. The data needs to be pushed to the upper layer. We can't rely on the timeout IRQ (RTOR) that can't be triggered into low power state. So safely clear DMA request (DMAR), force the DMA reception routines to push RX buffer content, before disabling RX DMA. This way, handover to pio mode is safe. Only call tty_flip_buffer_push() when there is RX data to handle. Move the locking outside of stm32_usart_receive_chars() to prevent a race condition, when disabling DMA request upon suspend / pm_runtime_suspend. Data may be received under IRQ and pushed before stm32_usart_receive_chars() has pushed older data from DMA rx_buf upon suspend. The sequence in suspend routine needs proper locking to avoid this. Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com> Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com> Link: https://lore.kernel.org/r/20211025134229.8456-4-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.