From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753737AbbAJAJI (ORCPT ); Fri, 9 Jan 2015 19:09:08 -0500 Received: from mail.kmu-office.ch ([178.209.48.109]:36856 "EHLO mail.kmu-office.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751947AbbAJAJG (ORCPT ); Fri, 9 Jan 2015 19:09:06 -0500 From: Stefan Agner To: gregkh@linuxfoundation.org Cc: jslaby@suse.cz, jingchang.lu@freescale.com, shawn.guo@linaro.org, linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, stefan@agner.ch Subject: [PATCH v2 2/2] serial: fsl_lpuart: avoid new transfer while DMA is running Date: Sat, 10 Jan 2015 01:08:59 +0100 Message-Id: <1420848539-4519-3-git-send-email-stefan@agner.ch> X-Mailer: git-send-email 2.2.1 In-Reply-To: <1420848539-4519-1-git-send-email-stefan@agner.ch> References: <1420848539-4519-1-git-send-email-stefan@agner.ch> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When the UART is in DMA receive mode (RDMAS set) and one character just arrived while another interrupt is handled (e.g. TX), the RDRF (receiver data register full flag) is set due to the water level of 1. But since the DMA will take care of this character, there is no need to handle it by calling lpuart_prepare_rx. Handling it leads to adding the RX timeout timer twice: [ 74.336698] Kernel BUG at 80053070 [verbose debug info unavailable] [ 74.342999] Internal error: Oops - BUG: 0 [#1] ARM0:00.00 khungtaskd [ 74.347817] Modules linked in: 0 S 0.0 0.0 0:00.00 writeback [ 74.350926] CPU: 0 PID: 0 Comm: swapper Not tainted 3.19.0-rc3-00001-g39d78e2 #1788 [ 74.358617] Hardware name: Freescale Vybrid VF610 (Device Tree)t [ 74.364563] task: 807a7678 ti: 8079c000 task.ti: 8079c000 kblockd [ 74.370002] PC is at add_timer+0x24/0x28.0 0.0 0:00.09 kworker/u2:1 [ 74.373960] LR is at lpuart_int+0x15c/0x3d8 [ 74.378171] pc : [<80053070>] lr : [<802e0d88>] psr: a0010193 [ 74.378171] sp : 8079de10 ip : 8079de20 fp : 8079de1c [ 74.389694] r10: 807d44c0 r9 : 8688c300 r8 : 00000013 [ 74.394943] r7 : 20010193 r6 : 00000000 r5 : 000000a0 r4 : 86997210 [ 74.401498] r3 : ffffa7da r2 : 80817868 r1 : 86997210 r0 : 86997344 [ 74.408052] Flags: NzCv IRQs off FIQs on Mode SVC_32 ISA ARM Segment kernel [ 74.415489] Control: 10c5387d Table: 8611c059 DAC: 00000015 [ 74.421265] Process swapper (pid: 0, stack limit = 0x8079c230) ... Solve this by only execute the receiver path (lpuart_prepare_rx) if the DMA receive mode (RDMAS) is not set. Also, make sure the flag is cleared on initialization, in case it has been left set. This can be best reproduced using UART as a serial console, then running top while dd'ing data into the terminal. Signed-off-by: Stefan Agner --- drivers/tty/serial/fsl_lpuart.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c index 29932b7..e95c497 100644 --- a/drivers/tty/serial/fsl_lpuart.c +++ b/drivers/tty/serial/fsl_lpuart.c @@ -755,18 +755,18 @@ out: static irqreturn_t lpuart_int(int irq, void *dev_id) { struct lpuart_port *sport = dev_id; - unsigned char sts; + unsigned char sts, crdma; sts = readb(sport->port.membase + UARTSR1); + crdma = readb(sport->port.membase + UARTCR5); - if (sts & UARTSR1_RDRF) { + if (sts & UARTSR1_RDRF && !(crdma & UARTCR5_RDMAS)) { if (sport->lpuart_dma_use) lpuart_prepare_rx(sport); else lpuart_rxint(irq, dev_id); } - if (sts & UARTSR1_TDRE && - !(readb(sport->port.membase + UARTCR5) & UARTCR5_TDMAS)) { + if (sts & UARTSR1_TDRE && !(crdma & UARTCR5_TDMAS)) { if (sport->lpuart_dma_use) lpuart_pio_tx(sport); else @@ -1106,6 +1106,7 @@ static int lpuart_startup(struct uart_port *port) setup_timer(&sport->lpuart_timer, lpuart_timer_func, (unsigned long)sport); temp = readb(port->membase + UARTCR5); + temp &= ~UARTCR5_RDMAS; writeb(temp | UARTCR5_TDMAS, port->membase + UARTCR5); } -- 2.2.1 From mboxrd@z Thu Jan 1 00:00:00 1970 From: stefan@agner.ch (Stefan Agner) Date: Sat, 10 Jan 2015 01:08:59 +0100 Subject: [PATCH v2 2/2] serial: fsl_lpuart: avoid new transfer while DMA is running In-Reply-To: <1420848539-4519-1-git-send-email-stefan@agner.ch> References: <1420848539-4519-1-git-send-email-stefan@agner.ch> Message-ID: <1420848539-4519-3-git-send-email-stefan@agner.ch> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org When the UART is in DMA receive mode (RDMAS set) and one character just arrived while another interrupt is handled (e.g. TX), the RDRF (receiver data register full flag) is set due to the water level of 1. But since the DMA will take care of this character, there is no need to handle it by calling lpuart_prepare_rx. Handling it leads to adding the RX timeout timer twice: [ 74.336698] Kernel BUG at 80053070 [verbose debug info unavailable] [ 74.342999] Internal error: Oops - BUG: 0 [#1] ARM0:00.00 khungtaskd [ 74.347817] Modules linked in: 0 S 0.0 0.0 0:00.00 writeback [ 74.350926] CPU: 0 PID: 0 Comm: swapper Not tainted 3.19.0-rc3-00001-g39d78e2 #1788 [ 74.358617] Hardware name: Freescale Vybrid VF610 (Device Tree)t [ 74.364563] task: 807a7678 ti: 8079c000 task.ti: 8079c000 kblockd [ 74.370002] PC is at add_timer+0x24/0x28.0 0.0 0:00.09 kworker/u2:1 [ 74.373960] LR is at lpuart_int+0x15c/0x3d8 [ 74.378171] pc : [<80053070>] lr : [<802e0d88>] psr: a0010193 [ 74.378171] sp : 8079de10 ip : 8079de20 fp : 8079de1c [ 74.389694] r10: 807d44c0 r9 : 8688c300 r8 : 00000013 [ 74.394943] r7 : 20010193 r6 : 00000000 r5 : 000000a0 r4 : 86997210 [ 74.401498] r3 : ffffa7da r2 : 80817868 r1 : 86997210 r0 : 86997344 [ 74.408052] Flags: NzCv IRQs off FIQs on Mode SVC_32 ISA ARM Segment kernel [ 74.415489] Control: 10c5387d Table: 8611c059 DAC: 00000015 [ 74.421265] Process swapper (pid: 0, stack limit = 0x8079c230) ... Solve this by only execute the receiver path (lpuart_prepare_rx) if the DMA receive mode (RDMAS) is not set. Also, make sure the flag is cleared on initialization, in case it has been left set. This can be best reproduced using UART as a serial console, then running top while dd'ing data into the terminal. Signed-off-by: Stefan Agner --- drivers/tty/serial/fsl_lpuart.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c index 29932b7..e95c497 100644 --- a/drivers/tty/serial/fsl_lpuart.c +++ b/drivers/tty/serial/fsl_lpuart.c @@ -755,18 +755,18 @@ out: static irqreturn_t lpuart_int(int irq, void *dev_id) { struct lpuart_port *sport = dev_id; - unsigned char sts; + unsigned char sts, crdma; sts = readb(sport->port.membase + UARTSR1); + crdma = readb(sport->port.membase + UARTCR5); - if (sts & UARTSR1_RDRF) { + if (sts & UARTSR1_RDRF && !(crdma & UARTCR5_RDMAS)) { if (sport->lpuart_dma_use) lpuart_prepare_rx(sport); else lpuart_rxint(irq, dev_id); } - if (sts & UARTSR1_TDRE && - !(readb(sport->port.membase + UARTCR5) & UARTCR5_TDMAS)) { + if (sts & UARTSR1_TDRE && !(crdma & UARTCR5_TDMAS)) { if (sport->lpuart_dma_use) lpuart_pio_tx(sport); else @@ -1106,6 +1106,7 @@ static int lpuart_startup(struct uart_port *port) setup_timer(&sport->lpuart_timer, lpuart_timer_func, (unsigned long)sport); temp = readb(port->membase + UARTCR5); + temp &= ~UARTCR5_RDMAS; writeb(temp | UARTCR5_TDMAS, port->membase + UARTCR5); } -- 2.2.1