Hi, Geert-san, > From: Geert Uytterhoeven > Sent: Friday, May 27, 2016 3:19 AM > > Make sure the transmitter and receiver are stopped when shutting down > the port, and related interrupts are disabled. > > Without this: > - New input data may be received into the RX FIFO, possibly > triggering a new RX DMA completion, > - Transfers will still be enabled on a subsequent startup of the UART, > before the UART's FIFOs have been reset, causing reading of stale > data. > > Inspired by a patch in the BSP by Koji Matsuoka > <koji.matsuoka.xm@xxxxxxxxxxx>. > > Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx> > --- > Extracted from "[PATCH/RFC v3 0/4] serial: sh-sci: Add DT DMA support". > The issues with the serial console seen before on r8a7740/armadillo and > sh73a0/kzm9g seem to be gone. > > Changes after resurrection: > - Write zero to also disable related interrupts, as suggested by > Laurent Pinchart, If we write zero to the register, we cannot use the port as a console after it is called. In fact, I have an issue while rc scripts are running on my root filesystem. When rc scripts is running, "shutdown" is called a lot. After the "shutdown", if the kernel will put strings using a console, it cannot put strings because the register is zero (TE and CKE are 0). So, we have to consider it. FYI, I made a patch to fix this issue. (Perhaps, both the CKE and TE should be set in the serial_console_write(), but I don't know how to set the CKE for now :) ) Best regards, Yoshihiro Shimoda --- diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c index afa25ec..b5b1b38 100644 --- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -1989,6 +1989,7 @@ static void sci_shutdown(struct uart_port *port) { struct sci_port *s = to_sci_port(port); unsigned long flags; + unsigned int ctrl; dev_dbg(port->dev, "%s(%d)\n", __func__, port->line); @@ -1998,8 +1999,12 @@ static void sci_shutdown(struct uart_port *port) spin_lock_irqsave(&port->lock, flags); sci_stop_rx(port); sci_stop_tx(port); - /* Stop RX and TX, disable related interrupts */ - serial_port_out(port, SCSCR, 0); + /* Stop RX and TX, disable related interrupts, keep clock source */ + ctrl = serial_port_in(port, SCSCR); + ctrl = (s->cfg->scscr & ~(SCSCR_CKE1 | SCSCR_CKE0)) | + (ctrl & (SCSCR_CKE1 | SCSCR_CKE0)); + serial_port_out(port, SCSCR, ctrl); + spin_unlock_irqrestore(&port->lock, flags); #ifdef CONFIG_SERIAL_SH_SCI_DMA @@ -2801,6 +2806,8 @@ static void serial_console_write(struct console *co, const char *s, ctrl = serial_port_in(port, SCSCR); ctrl_temp = (sci_port->cfg->scscr & ~(SCSCR_CKE1 | SCSCR_CKE0)) | (ctrl & (SCSCR_CKE1 | SCSCR_CKE0)); + ctrl_temp |= SCSCR_TE; /* FIXME: while "break ctl" is on */ + serial_port_out(port, SCSCR, ctrl_temp); uart_console_write(port, s, count, serial_console_putchar); -- 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