From patchwork Fri Aug 15 17:42:38 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sebastian Andrzej Siewior X-Patchwork-Id: 4728791 Return-Path: X-Original-To: patchwork-linux-omap@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 3C43FC0338 for ; Fri, 15 Aug 2014 18:04:51 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 6D7FB201F2 for ; Fri, 15 Aug 2014 18:04:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 86E232016C for ; Fri, 15 Aug 2014 18:04:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751364AbaHOSEd (ORCPT ); Fri, 15 Aug 2014 14:04:33 -0400 Received: from www.linutronix.de ([62.245.132.108]:57819 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751027AbaHOSEc (ORCPT ); Fri, 15 Aug 2014 14:04:32 -0400 Received: from localhost ([127.0.0.1] helo=bazinga.breakpoint.cc) by Galois.linutronix.de with esmtp (Exim 4.80) (envelope-from ) id 1XILWi-0006sE-VZ; Fri, 15 Aug 2014 19:42:57 +0200 From: Sebastian Andrzej Siewior To: linux-serial@vger.kernel.org Cc: linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org, tony@atomide.com, balbi@ti.com, Vinod Koul , Greg Kroah-Hartman , Sebastian Andrzej Siewior Subject: [PATCH 10/15] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx Date: Fri, 15 Aug 2014 19:42:38 +0200 Message-Id: <1408124563-31541-11-git-send-email-bigeasy@linutronix.de> X-Mailer: git-send-email 2.0.1 In-Reply-To: <1408124563-31541-1-git-send-email-bigeasy@linutronix.de> References: <1408124563-31541-1-git-send-email-bigeasy@linutronix.de> X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1, SHORTCIRCUIT=-0.0001 Sender: linux-omap-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-omap@vger.kernel.org X-Spam-Status: No, score=-7.6 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP At least on AM335x the following problem exists: Even if the TX FIFO is empty and a TX transfer is programmed (and started) the UART does not trigger the DMA transfer. After $TRESHOLD number of bytes have been written to the FIFO manually the UART reevaluates the whole situation and decides that now there is enough room in the FIFO and so the transfer begins. This problem has not been seen on DRA7 or beaglebone (OMAP3). The workaround is to use a threshold of one byte, program the DMA transfer minus one byte and then to put the first byte into the FIFO to kick start the transfer. Signed-off-by: Sebastian Andrzej Siewior --- drivers/tty/serial/8250/8250.h | 1 + drivers/tty/serial/8250/8250_dma.c | 18 +++++++++++++++--- 2 files changed, 16 insertions(+), 3 deletions(-) diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h index 1bcb4b2..d6a3f5c 100644 --- a/drivers/tty/serial/8250/8250.h +++ b/drivers/tty/serial/8250/8250.h @@ -79,6 +79,7 @@ struct serial8250_config { #define UART_BUG_NOMSR (1 << 2) /* UART has buggy MSR status bits (Au1x00) */ #define UART_BUG_THRE (1 << 3) /* UART has buggy THRE reassertion */ #define UART_BUG_PARITY (1 << 4) /* UART mishandles parity if FIFO enabled */ +#define UART_BUG_DMATX (1 << 5) /* UART needs one byte in FIFO for kickstart */ #define PROBE_RSA (1 << 0) #define PROBE_ANY (~0) diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c index 7417ed5..dc1294b 100644 --- a/drivers/tty/serial/8250/8250_dma.c +++ b/drivers/tty/serial/8250/8250_dma.c @@ -83,6 +83,7 @@ int serial8250_tx_dma(struct uart_8250_port *p) struct uart_8250_dma *dma = p->dma; struct circ_buf *xmit = &p->port.state->xmit; struct dma_async_tx_descriptor *desc; + unsigned int skip_byte = 0; int ret; if (uart_tx_stopped(&p->port) || dma->tx_running || @@ -91,10 +92,18 @@ int serial8250_tx_dma(struct uart_8250_port *p) dma->tx_size = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE); + if (p->bugs & UART_BUG_DMATX) { + if (dma->tx_size < 4) { + ret = -EINVAL; + goto err; + } + skip_byte = 1; + } + desc = dmaengine_prep_slave_single(dma->txchan, - dma->tx_addr + xmit->tail, - dma->tx_size, DMA_MEM_TO_DEV, - DMA_PREP_INTERRUPT | DMA_CTRL_ACK); + dma->tx_addr + xmit->tail + skip_byte, + dma->tx_size - skip_byte, DMA_MEM_TO_DEV, + DMA_PREP_INTERRUPT | DMA_CTRL_ACK); if (!desc) { ret = -EBUSY; goto err; @@ -118,6 +127,9 @@ int serial8250_tx_dma(struct uart_8250_port *p) serial_out(p, UART_IER, p->ier); } } + if (skip_byte) + serial_out(p, UART_TX, xmit->buf[xmit->tail]); + return 0; err: p->dma_tx_err = 1;