Hi all, on an i.MX6Q we had a situation where we got "Imprecise Data Aborts". The backtraces of those aborts were useless, all over the place. But we found out that we can trigger this bug with this procedure: - make some external PC send constantly through the serial port to the i.MX6Q. - run a serial program on the i.MX6Q that receives the data and echos it back - let this program terminate and restart every over second (we used a 4 second interval) Chances were good that we reproduced the issue with various kernels (up to 4.7.2). In the drivers/tty/serial/tty/imx.c I disabled all DMA, because this was my first suspicion. But to no avail. Eventually we asked some company to help us. They produced the following patch. With this patch, we can now run for a long time without any imprecise data abort (actually we run into another issue, but according to https://lkml.org/lkml/2016/5/16/452 "tty crash in Linux 4.6" this is already in the working). It's entirely clear to me that below WIP-patch has ZERO chance of being added. It's not just checkpatch that will barf over it. :-) My goal is to make the more knowledgeable people aware of the issue and to give them a pointer, so that they can tell me how to fix the issue in a correct way. Holger --- linux-4.6.orig/drivers/tty/serial/imx.c +++ linux-4.6/drivers/tty/serial/imx.c @@ -234,6 +234,9 @@ unsigned int ucr3; }; +static unsigned int DBG_Starttx = 0; +atomic_t imx_uart_is_in_irq = ATOMIC_INIT(0); + static struct imx_uart_data imx_uart_devdata[] = { [IMX1_UART] = { .uts_reg = IMX1_UTS, @@ -386,8 +389,8 @@ } } - temp = readl(sport->port.membase + UCR2); - writel(temp & ~UCR2_RXEN, sport->port.membase + UCR2); + //temp = readl(sport->port.membase + UCR2); + //writel(temp & ~UCR2_RXEN, sport->port.membase + UCR2); /* disable the `Receiver Ready Interrrupt` */ temp = readl(sport->port.membase + UCR1); @@ -577,6 +580,7 @@ } if (!sport->dma_is_enabled) { + //DBG_Starttx++; temp = readl(sport->port.membase + UCR1); writel(temp | UCR1_TXMPTYEN, sport->port.membase + UCR1); } spin_lock_irqsave(&sport->port.lock, flags); while (readl(sport->port.membase + USR2) & USR2_RDR) { + //skip if not enabled + if(((readl(sport->port.membase + UCR2) & UCR2_RXEN) ==0 ) + || ((readl(sport->port.membase + UCR1) & UCR1_UARTEN) ==0 )) + goto out; + flg = TTY_NORMAL; sport->port.icount.rx++; + + rx = readl(sport->port.membase + URXD0); @@ -735,6 +746,7 @@ unsigned int sts; unsigned int sts2; + atomic_add(1,&imx_uart_is_in_irq); sts = readl(sport->port.membase + USR1); sts2 = readl(sport->port.membase + USR2); @@ -761,7 +773,7 @@ sport->port.icount.overrun++; writel(USR2_ORE, sport->port.membase + USR2); } - + atomic_sub(1,&imx_uart_is_in_irq); return IRQ_HANDLED; } @@ -896,6 +908,7 @@ struct imx_port *sport = (struct imx_port *)data; unsigned long flags; + atomic_add(1,&imx_uart_is_in_irq); if (sport->port.state) { spin_lock_irqsave(&sport->port.lock, flags); imx_mctrl_check(sport); @@ -903,6 +916,7 @@ mod_timer(&sport->timer, jiffies + MCTRL_TIMEOUT); } + atomic_sub(1,&imx_uart_is_in_irq); } #define RX_BUF_SIZE (PAGE_SIZE) @@ -1251,7 +1267,7 @@ } spin_lock_irqsave(&sport->port.lock, flags); imx_stop_tx(port); - imx_stop_rx(port); +// imx_stop_rx(port); imx_disable_dma(sport); spin_unlock_irqrestore(&sport->port.lock, flags); imx_uart_dma_exit(sport); @@ -1261,7 +1277,7 @@ spin_lock_irqsave(&sport->port.lock, flags); temp = readl(sport->port.membase + UCR2); - temp &= ~(UCR2_TXEN); + //temp &= ~(UCR2_TXEN); writel(temp, sport->port.membase + UCR2); spin_unlock_irqrestore(&sport->port.lock, flags); @@ -1276,13 +1292,16 @@ spin_lock_irqsave(&sport->port.lock, flags); temp = readl(sport->port.membase + UCR1); - temp &= ~(UCR1_TXMPTYEN | UCR1_RRDYEN | UCR1_RTSDEN | UCR1_UARTEN); + //temp &= ~(UCR1_TXMPTYEN | UCR1_RRDYEN | UCR1_RTSDEN | UCR1_UARTEN); + temp &= ~(UCR1_TXMPTYEN | UCR1_RRDYEN | UCR1_RTSDEN); writel(temp, sport->port.membase + UCR1); spin_unlock_irqrestore(&sport->port.lock, flags); - clk_disable_unprepare(sport->clk_per); - clk_disable_unprepare(sport->clk_ipg); + while(atomic_read(&imx_uart_is_in_irq) == 1); + + //clk_disable_unprepare(sport->clk_per); + //clk_disable_unprepare(sport->clk_ipg); } static void imx_flush_buffer(struct uart_port *port) @@ -1732,8 +1750,8 @@ if (locked) spin_unlock_irqrestore(&sport->port.lock, flags); - clk_disable(sport->clk_ipg); - clk_disable(sport->clk_per); + //clk_disable(sport->clk_ipg); + //clk_disable(sport->clk_per); } /* @@ -1834,7 +1852,7 @@ retval = uart_set_options(&sport->port, co, baud, parity, bits, flow); - clk_disable(sport->clk_ipg); + /*clk_disable(sport->clk_ipg); if (retval) { clk_unprepare(sport->clk_ipg); goto error_console; @@ -1843,7 +1861,7 @@ retval = clk_prepare(sport->clk_per); if (retval) clk_disable_unprepare(sport->clk_ipg); - + */ error_console: return retval; } @@ -2034,7 +2052,7 @@ UCR1_TXMPTYEN | UCR1_RTSDEN); writel_relaxed(reg, sport->port.membase + UCR1); - clk_disable_unprepare(sport->clk_ipg); + //clk_disable_unprepare(sport->clk_ipg); /* * Allocate the IRQ(s) i.MX1 has three interrupts whereas later @@ -2136,7 +2154,7 @@ serial_imx_save_context(sport); - clk_disable(sport->clk_ipg); + //clk_disable(sport->clk_ipg); return 0; } @@ -2153,7 +2171,7 @@ serial_imx_restore_context(sport); - clk_disable(sport->clk_ipg); + //clk_disable(sport->clk_ipg); return 0; } -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
