Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946595AbbHHA3F (ORCPT ); Fri, 7 Aug 2015 20:29:05 -0400 Received: from mail-qg0-f48.google.com ([209.85.192.48]:36548 "EHLO mail-qg0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1946550AbbHHA3C (ORCPT ); Fri, 7 Aug 2015 20:29:02 -0400 Message-ID: <55C54D49.3090406@hurleysoftware.com> Date: Fri, 07 Aug 2015 20:28:57 -0400 From: Peter Hurley User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.8.0 MIME-Version: 1.0 To: Sebastian Andrzej Siewior , Vinod Koul , Russell King CC: Dan Williams , dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, nsekhar@ti.com, linux-omap@vger.kernel.org, linux-serial@vger.kernel.org, john.ogness@linutronix.de, Peter Ujfalusi Subject: Re: [PATCH 1/3] tty: serial: 8250_omap: do not use RX DMA if pause is not supported References: <1438977619-15488-1-git-send-email-bigeasy@linutronix.de> <1438977619-15488-2-git-send-email-bigeasy@linutronix.de> In-Reply-To: <1438977619-15488-2-git-send-email-bigeasy@linutronix.de> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3037 Lines: 82 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: > Signed-off-by: Sebastian Andrzej Siewior > --- > 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-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/