tty: serial: fsl_lpuart: terminate DMA on buffer flush
On uart buffer flush, serial core resets the circular buffer. If a DMA transfer is in progress at that time, the callback lpuart_dma_tx_complete will move buffer's tail unconditionally, hence tail moves beyond head. Use the flush_buffer hook to terminate the DMA imeaditely and avoid lpuart_dma_tx_complete being called in this situation. This bug often showed up while shutdown and lead to duplicate serial console output. Signed-off-by: NStefan Agner <stefan@agner.ch> Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
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