Am 3. März 2020 19:47:37 MEZ schrieb Rob Herring [off-list ref]:

On Tue, Mar 03, 2020 at 06:43:00PM +0100, Michael Walle wrote:

quoted

The DMA channel might not be available at probe time. This is esp.

the

quoted

case if the DMA controller has an IOMMU mapping.

The subject should be updated as this doesn't involve deferred probe
any more. 

ok

quoted

There is also another caveat. If there is no DMA controller at all,
dma_request_chan() will also return -EPROBE_DEFER. Thus we cannot

test

quoted

for -EPROBE_DEFER in probe(). Otherwise the lpuart driver will fail

to

quoted

probe if, for example, the DMA driver is not enabled in the kernel
configuration.

To workaround this, we request the DMA channel in _startup(). Other
serial drivers do it the same way.

Signed-off-by: Michael Walle <redacted>
---
 drivers/tty/serial/fsl_lpuart.c | 84

+++++++++++++++++++++------------

quoted

 1 file changed, 53 insertions(+), 31 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c

b/drivers/tty/serial/fsl_lpuart.c

quoted

index c31b8f3db6bf..0b8c477b32a3 100644

--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c

@@ -1493,36 +1493,63 @@ static void rx_dma_timer_init(struct

lpuart_port *sport)

quoted

 static void lpuart_tx_dma_startup(struct lpuart_port *sport)
 {
 	u32 uartbaud;
+	int ret;
 
-	if (sport->dma_tx_chan && !lpuart_dma_tx_request(&sport->port)) {
-		init_waitqueue_head(&sport->dma_wait);
-		sport->lpuart_dma_tx_use = true;
-		if (lpuart_is_32(sport)) {
-			uartbaud = lpuart32_read(&sport->port, UARTBAUD);
-			lpuart32_write(&sport->port,
-				       uartbaud | UARTBAUD_TDMAE, UARTBAUD);
-		} else {
-			writeb(readb(sport->port.membase + UARTCR5) |
-				UARTCR5_TDMAS, sport->port.membase + UARTCR5);
-		}
+	sport->dma_tx_chan = dma_request_slave_channel(sport->port.dev,

"tx");

quoted

+	if (!sport->dma_tx_chan) {
+		dev_info_once(sport->port.dev,
+			      "DMA tx channel request failed, operating without tx

DMA\n");

Might be useful to print the errno too.

I didn't want to change the original error message. But I can change that when I update the subject. 

-michael


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