Am 3. März 2020 19:47:37 MEZ schrieb Rob Herring <robh@xxxxxxxxxx>:
>On Tue, Mar 03, 2020 at 06:43:00PM +0100, Michael Walle wrote:
>> The DMA channel might not be available at probe time. This is esp.
>the
>> case if the DMA controller has an IOMMU mapping.
>
>The subject should be updated as this doesn't involve deferred probe
>any more.
ok
>
>> 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
>> for -EPROBE_DEFER in probe(). Otherwise the lpuart driver will fail
>to
>> 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 <michael@xxxxxxxx>
>> ---
>> drivers/tty/serial/fsl_lpuart.c | 84
>+++++++++++++++++++++------------
>> 1 file changed, 53 insertions(+), 31 deletions(-)
>>
>> diff --git a/drivers/tty/serial/fsl_lpuart.c
>b/drivers/tty/serial/fsl_lpuart.c
>> 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)
>> 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");
>> + 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
