From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hector Palacios Subject: Re: [PATCH] serial: mxs-auart: wait for DMA buffer to flush before shutdown Date: Wed, 2 Oct 2013 09:31:16 +0200 Message-ID: <524BCBC4.5050708@digi.com> References: <1380644315-31581-1-git-send-email-hector.palacios@digi.com> <20131001194800.GL2548@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mail1.bemta7.messagelabs.com ([216.82.254.108]:56224 "EHLO mail1.bemta7.messagelabs.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752784Ab3JBHb3 (ORCPT ); Wed, 2 Oct 2013 03:31:29 -0400 In-Reply-To: <20131001194800.GL2548@pengutronix.de> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: =?ISO-8859-1?Q?Uwe_Kleine-K=F6nig?= Cc: "linux-serial@vger.kernel.org" , "b32955@freescale.com" , "gregkh@linuxfoundation.org" , "shawn.guo@linaro.org" , "fabio.estevam@freescale.com" , "marex@denx.de" Hello Uwe, On 10/01/2013 09:48 PM, Uwe Kleine-K=F6nig wrote: > Hello Hector, > > On Tue, Oct 01, 2013 at 06:18:35PM +0200, Hector Palacios wrote: >> The shutdown function was not waiting for the DMA buffer to flush >> before disabling the AUART. This lead to many bytes not being >> transferred (specially at low baudrates), as they were still in the >> DMA buffer when the AUART was shutdown. >> This patch also adds the check for the BUSY flag. >> >> Signed-off-by: Hector Palacios >> >> https://jira.digi.com/browse/DEL-616 > What is this? This isn't available in public DNS. Sorry, copy&paste error. I'll remove it. >> --- >> drivers/tty/serial/mxs-auart.c | 16 +++++++++++++++- >> 1 file changed, 15 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs= -auart.c >> index f85b8e6..0d8b2ca 100644 >> --- a/drivers/tty/serial/mxs-auart.c >> +++ b/drivers/tty/serial/mxs-auart.c >> @@ -750,12 +750,26 @@ static int mxs_auart_startup(struct uart_port = *u) >> return 0; >> } >> >> +static unsigned int mxs_auart_tx_empty(struct uart_port *u); >> + >> static void mxs_auart_shutdown(struct uart_port *u) >> { >> struct mxs_auart_port *s =3D to_auart_port(u); >> + unsigned int to; >> + >> + if (auart_dma_enabled(s)) { >> + /* Wait enough time to flush DMA buffer completely */ >> + to =3D u->timeout * UART_XMIT_SIZE / u->fifosize; > u->timeout is the time needed to send one char, right? UART_XMIT_SIZE= is > the size of the circular buffer, fifosize is the size of the fifo. I > don't get what you get by dividing by the fifosize. I would have > expected something like: > > u->timeout * min(UART_XMIT_SIZE, u->fifosize) > > Can you explain, maybe in a comment along the code for the next perso= n > not understanding? u->timeout is *not* the time needed to send one char but the time neede= d to flush the=20 complete port fifo (see uart_update_timeout() in serial_core.c where it= is set). UART_XMIT_SIZE is the number of bytes in the DMA buffer, so I divide th= e max number of=20 bytes in the FIFO by the FIFO size and multiply by the FIFO timeout. > I wonder if the individual driver is the right place this must be fix= ed > in or if there should be (or even exists) some help form the serial > framework?! Good question, the issue should exit in other DMA drivers as well. Best regards, -- Hector Palacios -- To unsubscribe from this list: send the line "unsubscribe linux-serial"= in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html