On 08/07/2015 11:00 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: <sta...@vger.kernel.org>
> Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
> ---
> 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;
I don't think this is good thing for the stable _and_ for the mainline at the
same time:
in stable the rx DMA should not be allowed since the stable kernels does not
allow pause/resume with omap-dma, so there the rx DMA should be just disabled
for UART. This change will cause regression since it introduce a WARN_ON_ONCE,
which will be printed if the user tries to use non working feature.
In mainline you will eventually going to have pause/resume support so this
patch will make no sense there.
>
> 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)
>
--
Péter
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