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.
> 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.
Rob
