>
> Andy
>> >
>> > 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>
>>
>> This appears to cause boot hangs on imx8qxp-mek (boards boots fine on
>> next-20200324 if this patch is reverted)
>>
>> > ---
>> > drivers/tty/serial/fsl_lpuart.c | 88
+++++++++++++++++++++------------
>> > 1 file changed, 57 insertions(+), 31 deletions(-)
>> >
>> > diff --git a/drivers/tty/serial/fsl_lpuart.c
>> > b/drivers/tty/serial/fsl_lpuart.c index c31b8f3db6bf..33798df4d727
>> > 100644
>> > --- a/drivers/tty/serial/fsl_lpuart.c
>> > +++ b/drivers/tty/serial/fsl_lpuart.c
>> > @@ -1493,36 +1493,67 @@ 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_chan(sport->port.dev, "tx");
>> > + if (IS_ERR(sport->dma_tx_chan)) {
>> > + dev_info_once(sport->port.dev,
>> > + "DMA tx channel request failed, operating
>> > + without tx
>> DMA (%ld)\n",
>> > + PTR_ERR(sport->dma_tx_chan));
>>
>> It seems that this since this is called from lpuart32_startup with
>> &sport->port.lock held and lpuart32_console_write takes the same lock
>> it can and hang.
>>
>> As a workaround I can just remove this print but there are other
>> possible error conditions in dmaengine code which can cause a printk.
>>
>> Maybe the port lock should only be held around register manipulation?
>>
>> > + sport->dma_tx_chan = NULL;
>> > + goto err;
>> > + }
>> > +
>> > + ret = lpuart_dma_tx_request(&sport->port);
>> > + if (!ret)
>> > + goto err;
>>
>> This is backwards: lpuart_dma_tx_request returns negative errno on
>> failure.
>>
>> > +
>> > + 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 {
>> > - sport->lpuart_dma_tx_use = false;
>> > + writeb(readb(sport->port.membase + UARTCR5) |
>> > + UARTCR5_TDMAS, sport->port.membase +
UARTCR5);
>> > }
>> > +
>> > + return;
>> > +
>> > +err:
>> > + sport->lpuart_dma_tx_use = false;
>> > }
>> >
>> > static void lpuart_rx_dma_startup(struct lpuart_port *sport)
>> > {
>> > - if (sport->dma_rx_chan && !lpuart_start_rx_dma(sport)) {
>> > - /* set Rx DMA timeout */
>> > - sport->dma_rx_timeout =
msecs_to_jiffies(DMA_RX_TIMEOUT);
>> > - if (!sport->dma_rx_timeout)
>> > - sport->dma_rx_timeout = 1;
>> > + int ret;
>> >
>> > - sport->lpuart_dma_rx_use = true;
>> > - rx_dma_timer_init(sport);
>> > - } else {
>> > - sport->lpuart_dma_rx_use = false;
>> > + sport->dma_rx_chan = dma_request_chan(sport->port.dev, "rx");
>> > + if (IS_ERR(sport->dma_rx_chan)) {
>> > + dev_info_once(sport->port.dev,
>> > + "DMA rx channel request failed, operating
>> > + without rx
>> DMA (%ld)\n",
>> > + PTR_ERR(sport->dma_rx_chan));
>> > + sport->dma_rx_chan = NULL;
>> > + goto err;
>> > }
>> > +
>> > + ret = lpuart_start_rx_dma(sport); if (ret)
>> > + goto err;
>>
>> This is not backwards.
>>
>> > +
>> > + /* set Rx DMA timeout */
>> > + sport->dma_rx_timeout = msecs_to_jiffies(DMA_RX_TIMEOUT); if
>> > + (!sport->dma_rx_timeout)
>> > + sport->dma_rx_timeout = 1;
>> > +
>> > + sport->lpuart_dma_rx_use = true; rx_dma_timer_init(sport);
>> > +
>> > + return;
>> > +
>> > +err:
>> > + sport->lpuart_dma_rx_use = false;
>> > }
>> >
>> > static int lpuart_startup(struct uart_port *port) @@ -1615,6
>> > +1646,11 @@ static void lpuart_dma_shutdown(struct lpuart_port
>> > +*sport)
>> >
dmaengine_terminate_all(sport->dma_tx_chan);
>> > }
>> > }
>> > +
>> > + if (sport->dma_tx_chan)
>> > + dma_release_channel(sport->dma_tx_chan);
>> > + if (sport->dma_rx_chan)
>> > + dma_release_channel(sport->dma_rx_chan);
>> > }
>> >
>> > static void lpuart_shutdown(struct uart_port *port) @@ -2520,16
>> > +2556,6 @@ static int lpuart_probe(struct platform_device *pdev)
>> >
>> > sport->port.rs485_config(&sport->port, &sport->port.rs485);
>> >
>> > - sport->dma_tx_chan = dma_request_slave_channel(sport->port.dev,
>> "tx");
>> > - if (!sport->dma_tx_chan)
>> > - dev_info(sport->port.dev, "DMA tx channel request failed, "
>> > - "operating without tx DMA\n");
>> > -
>> > - sport->dma_rx_chan = dma_request_slave_channel(sport->port.dev,
>> "rx");
>> > - if (!sport->dma_rx_chan)
>> > - dev_info(sport->port.dev, "DMA rx channel request failed, "
>> > - "operating without rx DMA\n");
>> > -
>> > return 0;
>> >
>> > failed_attach_port:
>> >
