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FROMLIST: serial: qcom_geni: fix kfifo underflow when flush precede DMA completion IRQ #540

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FROMLIST: serial: qcom_geni: fix kfifo underflow when flush precede DMA completion IRQ #540

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14 changes: 13 additions & 1 deletion drivers/tty/serial/qcom_geni_serial.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1022,8 +1022,20 @@ static void qcom_geni_serial_handle_tx_dma(struct uart_port *uport)
{
struct qcom_geni_serial_port *port = to_dev_port(uport);
struct tty_port *tport = &uport->state->port;
unsigned int fifo_len = kfifo_len(&tport->xmit_fifo);

/*
* Only advance the kfifo if it still contains the bytes that were
* transferred. uart_flush_buffer() may have run before this IRQ
* fired: it calls kfifo_reset() under the port lock, making
* fifo_len = 0 while tx_remaining remains non-zero. Calling
* uart_xmit_advance() in that case would underflow kfifo->out past
* kfifo->in, making kfifo_len() wrap to UART_XMIT_SIZE - tx_remaining
* and triggering a spurious large DMA transfer of stale data.
*/
if (fifo_len >= port->tx_remaining)
uart_xmit_advance(uport, port->tx_remaining);

uart_xmit_advance(uport, port->tx_remaining);
geni_se_tx_dma_unprep(&port->se, port->tx_dma_addr, port->tx_remaining);
port->tx_dma_addr = 0;
port->tx_remaining = 0;
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