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serial: 8250_mtk: fix uart corruption issue when rx power off
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commit 7c4a509 upstream.

Fix uart corruption issue when rx power off.
Add spin lock in mtk8250_dma_rx_complete function in APDMA mode.

when uart is used as a communication port with external device(GPS).
when external device(GPS) power off, the power of rx pin is also from
1.8v to 0v. Even if there is not any data in rx. But uart rx pin can
capture the data "0".
If uart don't receive any data in specified cycle, uart will generates
BI(Break interrupt) interrupt.
If external device(GPS) power off, we found that BI interrupt appeared
continuously and very frequently.
When uart interrupt type is BI, uart IRQ handler(8250 framwork
API:serial8250_handle_irq) will push data to tty buffer.
mtk8250_dma_rx_complete is a task of mtk_uart_apdma_rx_handler.
mtk8250_dma_rx_complete priority is lower than uart irq
handler(serial8250_handle_irq).
if we are in process of mtk8250_dma_rx_complete, uart appear BI
interrupt:1)serial8250_handle_irq will priority execution.2)it may cause
write tty buffer conflict in mtk8250_dma_rx_complete.
So the spin lock protect the rx receive data process is not break.

Signed-off-by: Zhiyong Tao <zhiyong.tao@mediatek.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210729084640.17613-2-zhiyong.tao@mediatek.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Zhiyong Tao authored and gregkh committed Aug 12, 2021
1 parent b188f69 commit 19364ae
Showing 1 changed file with 5 additions and 0 deletions.
5 changes: 5 additions & 0 deletions drivers/tty/serial/8250/8250_mtk.c
Expand Up @@ -93,10 +93,13 @@ static void mtk8250_dma_rx_complete(void *param)
struct dma_tx_state state;
int copied, total, cnt;
unsigned char *ptr;
unsigned long flags;

if (data->rx_status == DMA_RX_SHUTDOWN)
return;

spin_lock_irqsave(&up->port.lock, flags);

dmaengine_tx_status(dma->rxchan, dma->rx_cookie, &state);
total = dma->rx_size - state.residue;
cnt = total;
Expand All @@ -120,6 +123,8 @@ static void mtk8250_dma_rx_complete(void *param)
tty_flip_buffer_push(tty_port);

mtk8250_rx_dma(up);

spin_unlock_irqrestore(&up->port.lock, flags);
}

static void mtk8250_rx_dma(struct uart_8250_port *up)
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