[PATCH] tty/serial/pl011: don't print error msg if dmaengine_pause is not supported

[PATCH] tty/serial/pl011: don't print error msg if dmaengine_pause is not supported

[Viresh Kumar]

Few dma controller doesn't support dmaengine_pause() and return -ENXIO if
dmaengine_pause() is called for them. Error messages such as "unable to pause
DMA transfer" shouldn't be printed for them.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
---
 drivers/tty/serial/amba-pl011.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 6deee4e..c0e1a42 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -755,18 +755,21 @@ static void pl011_dma_rx_irq(struct uart_amba_port *uap)
 	size_t pending;
 	struct dma_tx_state state;
 	enum dma_status dmastat;
+	int ret;
 
 	/*
 	 * Pause the transfer so we can trust the current counter,
 	 * do this before we pause the PL011 block, else we may
 	 * overflow the FIFO.
 	 */
-	if (dmaengine_pause(rxchan))
-		dev_err(uap->port.dev, "unable to pause DMA transfer\n");
+	ret = dmaengine_pause(rxchan);
+	if (ret && ret != -ENXIO)
+		dev_err(uap->port.dev, "unable to pause DMA transfer");
+
 	dmastat = rxchan->device->device_tx_status(rxchan,
-						   dmarx->cookie, &state);
-	if (dmastat != DMA_PAUSED)
-		dev_err(uap->port.dev, "unable to pause DMA transfer\n");
+			dmarx->cookie, &state);
+	if (ret != -ENXIO && dmastat != DMA_PAUSED)
+		dev_err(uap->port.dev, "unable to pause DMA transfer");
 
 	/* Disable RX DMA - incoming data will wait in the FIFO */
 	uap->dmacr &= ~UART011_RXDMAE;
-- 
1.7.2.2

[PATCH] tty/serial/pl011: don't print error msg if dmaengine_pause is not supported

[Russell King - ARM Linux]

On Mon, Apr 18, 2011 at 04:52:00PM +0530, Viresh Kumar wrote:
> Few dma controller doesn't support dmaengine_pause() and return -ENXIO if
> dmaengine_pause() is called for them. Error messages such as "unable to pause
> DMA transfer" shouldn't be printed for them.

It is _required_ to pause the DMA engine at this point, as we need to
read characters via PIO.  Leaving the DMA engine active at this point
invites it to transfer additional characters beneath us, before we've
had time to properly update the DMA engine for the characters received.

So, dmaengine_pause() is a requirement for PL011.

[PATCH] tty/serial/pl011: don't print error msg if dmaengine_pause is not supported

[viresh kumar]

On 04/18/2011 08:43 PM, Russell King - ARM Linux wrote:
> On Mon, Apr 18, 2011 at 04:52:00PM +0530, Viresh Kumar wrote:
>> Few dma controller doesn't support dmaengine_pause() and return -ENXIO if
>> dmaengine_pause() is called for them. Error messages such as "unable to pause
>> DMA transfer" shouldn't be printed for them.
> 
> It is _required_ to pause the DMA engine at this point, as we need to
> read characters via PIO.  Leaving the DMA engine active at this point
> invites it to transfer additional characters beneath us, before we've
> had time to properly update the DMA engine for the characters received.
> 
> So, dmaengine_pause() is a requirement for PL011.
> .
> 

Ok.

[PATCH] tty/serial/pl011: don't print error msg if dmaengine_pause is not supported

[Linus Walleij]

2011/4/18 Viresh Kumar <viresh.kumar@st.com>:

> Few dma controller doesn't support dmaengine_pause() and return -ENXIO if
> dmaengine_pause() is called for them. Error messages such as "unable to pause
> DMA transfer" shouldn't be printed for them.

Hm for dw_dma this seems like a piece of cake to simply implement
instead.

I'll send a patch for that instead, can you test it and ACK it if it
works for you?

Yours,
Linus Walleij