2012-02-20 01:24:42

by Chanho Min

Subject: [PATCH] amba-pl011​/dma: Add check for the residue in DMA callback

In DMA-operated uart, I found that rx data can be taken by the UART
interrupts during the DMA irq handler. pl011_int is occurred just
before it goes inside spin_lock_irq. When it returns to the callback,
DMA buffer already has been flushed. Then, pl011_dma_rx_chars gets
invalid data. So I add check for the residue as the patch bellow.

Signed-off-by: Chanho Min <[email protected]>
---
drivers/tty/serial/amba-pl011.c | 17 ++++++++++++++++-
1 files changed, 16 insertions(+), 1 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 6800f5f..cc3ea06 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -827,7 +827,12 @@ static void pl011_dma_rx_callback(void *data)
{
struct uart_amba_port *uap = data;
struct pl011_dmarx_data *dmarx = &uap->dmarx;
+ struct dma_chan *rxchan = dmarx->chan;
bool lastbuf = dmarx->use_buf_b;
+ struct pl011_sgbuf *sgbuf = dmarx->use_buf_b ?
+ &dmarx->sgbuf_b : &dmarx->sgbuf_a;
+ size_t pending;
+ struct dma_tx_state state;
int ret;

/*
@@ -838,11 +843,21 @@ static void pl011_dma_rx_callback(void *data)
* we immediately trigger the next DMA job.
*/
spin_lock_irq(&uap->port.lock);
+ /*
+ * Rx data can be taken by the UART interrupts during
+ * the DMA irq handler. So we check the residue here.
+ */
+ rxchan->device->device_tx_status(rxchan, dmarx->cookie, &state);
+ pending = sgbuf->sg.length - state.residue;
+ BUG_ON(pending > PL011_DMA_BUFFER_SIZE);
+ /* Then we terminate the transfer - we now know our residue */
+ dmaengine_terminate_all(rxchan);
+
uap->dmarx.running = false;
dmarx->use_buf_b = !lastbuf;
ret = pl011_dma_rx_trigger_dma(uap);

- pl011_dma_rx_chars(uap, PL011_DMA_BUFFER_SIZE, lastbuf, false);
+ pl011_dma_rx_chars(uap, pending, lastbuf, false);
spin_unlock_irq(&uap->port.lock);
/*
* Do this check after we picked the DMA chars so we don't
--
1.7.0.4

2012-02-20 08:31:24

by Linus Walleij

Subject: Re: [PATCH] amba-pl011​/dma: Add check for the res idue in DMA callback

On Mon, Feb 20, 2012 at 2:24 AM, Chanho Min <[email protected]> wrote:

> In DMA-operated uart, I found that rx data can be taken by the UART
> interrupts during the DMA irq handler. pl011_int is occurred just
> before it goes inside spin_lock_irq. When it returns to the callback,
> DMA buffer already has been flushed. Then, pl011_dma_rx_chars gets
> invalid data. So I add check for the residue as the patch bellow.
>
> Signed-off-by: Chanho Min <[email protected]>

Looks correct!
Acked-by: Linus Walleij <[email protected]>

Thanks,
Linus Walleij