Hi, Am 17.11.20 um 09:14 schrieb Stefan Wahren: > Hi, > > we are using a Modbus application on our customer i.MX6ULL board (RS-485 > in hardware, no DMA). While porting the board support package to a > Mainline kernel, we noticed that after boot the initial UART receive > causes IO errors, which breaks our application (tested with Mainline > 4.9, 4.19, 5.7, 5.9 but without success). The ancient vendor kernel > (imx-4.9.11) we are still using isn't affect by this issue. > > So i bisected the vendor tree and found this huge patch which fixed the > issue [1]. After that i was able to narrow down the fix to the following > patch against Mainline Linux 5.9 (successful tested on i.MX6ULL): > > diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c > index 07974f2..3004b5c 100644 > --- a/drivers/tty/serial/imx.c > +++ b/drivers/tty/serial/imx.c > @@ -1289,6 +1289,7 @@ static void imx_uart_clear_rx_errors(struct > imx_port *sport) > > #define TXTL_DEFAULT 2 /* reset default */ > #define RXTL_DEFAULT 1 /* reset default */ > +#define RXTL_UART 16 /* For UART */ > #define TXTL_DMA 8 /* DMA burst setting */ > #define RXTL_DMA 9 /* DMA burst setting */ > > @@ -1415,6 +1416,7 @@ static int imx_uart_startup(struct uart_port *port) > unsigned long flags; > int dma_is_inited = 0; > u32 ucr1, ucr2, ucr3, ucr4; > + unsigned char rx_fifo_trig; > > retval = clk_prepare_enable(sport->clk_per); > if (retval) > @@ -1425,7 +1427,12 @@ static int imx_uart_startup(struct uart_port *port) > return retval; > } > > - imx_uart_setup_ufcr(sport, TXTL_DEFAULT, RXTL_DEFAULT); > + if (uart_console(&sport->port)) > + rx_fifo_trig = RXTL_DEFAULT; > + else > + rx_fifo_trig = RXTL_UART; > + > + imx_uart_setup_ufcr(sport, TXTL_DEFAULT, rx_fifo_trig); > > /* disable the DREN bit (Data Ready interrupt enable) before > * requesting IRQs > @@ -1674,7 +1681,7 @@ imx_uart_set_termios(struct uart_port *port, > struct ktermios *termios, > * except those we will or may need to preserve. > */ > old_ucr2 = imx_uart_readl(sport, UCR2); > - ucr2 = old_ucr2 & (UCR2_TXEN | UCR2_RXEN | UCR2_ATEN | UCR2_CTS); > + ucr2 = old_ucr2 & (UCR2_TXEN | UCR2_RXEN | UCR2_CTS); > > ucr2 |= UCR2_SRST | UCR2_IRTS; > if ((termios->c_cflag & CSIZE) == CS8) > @@ -1795,6 +1802,9 @@ imx_uart_set_termios(struct uart_port *port, > struct ktermios *termios, > if (UART_ENABLE_MS(&sport->port, termios->c_cflag)) > imx_uart_enable_ms(&sport->port); > > + ucr2 = imx_uart_readl(sport, UCR2); > + imx_uart_writel(sport, ucr2 | UCR2_ATEN, UCR2); > + > spin_unlock_irqrestore(&sport->port.lock, flags); > } > > So i someone with a deeper insight can fix this properly. the issue still exists in Linux 5.10 rc6. > > Thanks Stefan > > [1] - > https://source.codeaurora.org/external/imx/linux-imx/commit/drivers/tty/serial/imx.c?h=imx_4.9.11_1.0.0_ga&id=e287334648e0a0f6a76f3d9615eada6cd590cbd9 > >
