On 08/07/2015 04:00 PM, Sebastian Andrzej Siewior wrote: > The 8250-omap driver requires the DMA-engine driver to support the pause > command in order to properly turn off programmed RX transfer before the > driver stars manually reading from the FIFO. > The lacking support of the requirement has been discovered recently. In > order to stay safe here we disable support for RX-DMA as soon as we > notice that it does not work. This should happen very early. > If the user does not want to see this backtrace he can either disable > DMA support (completely or RX-only) or backport the required patches for > edma / omap-dma once they hit mainline. > > Cc: <stable@xxxxxxxxxxxxxxx> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > --- > drivers/tty/serial/8250/8250_omap.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c > index 0340ee6ba970..07a11e0935e4 100644 > --- a/drivers/tty/serial/8250/8250_omap.c > +++ b/drivers/tty/serial/8250/8250_omap.c > @@ -112,6 +112,7 @@ struct omap8250_priv { > struct work_struct qos_work; > struct uart_8250_dma omap8250_dma; > spinlock_t rx_dma_lock; > + bool rx_dma_broken; > }; > > static u32 uart_read(struct uart_8250_port *up, u32 reg) > @@ -761,6 +762,7 @@ static void omap_8250_rx_dma_flush(struct uart_8250_port *p) > struct omap8250_priv *priv = p->port.private_data; > struct uart_8250_dma *dma = p->dma; > unsigned long flags; > + int ret; > > spin_lock_irqsave(&priv->rx_dma_lock, flags); > > @@ -769,7 +771,9 @@ static void omap_8250_rx_dma_flush(struct uart_8250_port *p) > return; > } > > - dmaengine_pause(dma->rxchan); > + ret = dmaengine_pause(dma->rxchan); > + if (WARN_ON_ONCE(ret)) > + priv->rx_dma_broken = true; No offense, Sebastian, but it boggles my mind that anyone could defend this as solid api design. We're in the middle of an interrupt handler and the slave dma driver is /just/ telling us now that it doesn't implement this functionality?!!? The dmaengine api has _so much_ setup and none of it contemplates telling the consumer that critical functionality is missing? Even dma_get_slave_caps() returns _true_ for cmd_pause support; ok, that interface is pointless. Rather than losing /critical data/ here, the interrupt handler should just busy-wait until dmaengine_tx_status() returns DMA_COMPLETE for the rx_cookie. Regards, Peter Hurley > spin_unlock_irqrestore(&priv->rx_dma_lock, flags); > > @@ -813,6 +817,9 @@ static int omap_8250_rx_dma(struct uart_8250_port *p, unsigned int iir) > break; > } > > + if (priv->rx_dma_broken) > + return -EINVAL; > + > spin_lock_irqsave(&priv->rx_dma_lock, flags); > > if (dma->rx_running) > -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html