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serial: sh-sci: Fix race condition causing garbage during shutdown

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If DMA is enabled and used, a burst of old data may be seen on the
serial console during "poweroff" or "reboot".  uart_flush_buffer()
clears the circular buffer, but sci_port.tx_dma_len is not reset.
This leads to a circular buffer overflow, dumping (UART_XMIT_SIZE -
sci_port.tx_dma_len) bytes.

To fix this, add a .flush_buffer() callback that resets
sci_port.tx_dma_len.

Inspired by commit 31ca2c63fdc0aee7 ("tty/serial: atmel: fix race
condition (TX+DMA)").

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Geert Uytterhoeven 2017-04-25 20:15:35 +02:00 committed by Greg Kroah-Hartman
parent 7fbcf3afe6
commit 1cf4a7efdc
1 changed files with 14 additions and 2 deletions
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16
drivers/tty/serial/sh-sci.c
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@ -1558,7 +1558,16 @@ static void sci_free_dma(struct uart_port *port)
if (s->chan_rx)
sci_rx_dma_release(s, false);
}
#else
static void sci_flush_buffer(struct uart_port *port)
{
/*
* In uart_flush_buffer(), the xmit circular buffer has just been
* cleared, so we have to reset tx_dma_len accordingly.
*/
to_sci_port(port)->tx_dma_len = 0;
}
#else /* !CONFIG_SERIAL_SH_SCI_DMA */
static inline void sci_request_dma(struct uart_port *port)
{
}
@ -1566,7 +1575,9 @@ static inline void sci_request_dma(struct uart_port *port)
static inline void sci_free_dma(struct uart_port *port)
{
}
#endif
#define sci_flush_buffer NULL
#endif /* !CONFIG_SERIAL_SH_SCI_DMA */
static irqreturn_t sci_rx_interrupt(int irq, void *ptr)
{
@ -2581,6 +2592,7 @@ static const struct uart_ops sci_uart_ops = {
.break_ctl = sci_break_ctl,
.startup = sci_startup,
.shutdown = sci_shutdown,
.flush_buffer = sci_flush_buffer,
.set_termios = sci_set_termios,
.pm = sci_pm,
.type = sci_type,