From: Al Cooper alcooperx@gmail.com
[ Upstream commit 9cabe26e65a893afd5846908aa393bd283ab6609 ]
There is a small window in time during resume where the hardware flow control signal RTS can be asserted (which allows a sender to resume sending data to the UART) but the baud rate has not yet been restored. This will cause corrupted data and FRAMING, OVERRUN and BREAK errors. This is happening because the MCTRL register is shadowed in uart_port struct and is later used during resume to set the MCTRL register during both serial8250_do_startup() and uart_resume_port(). Unfortunately, serial8250_do_startup() happens before the UART baud rate is restored. The fix is to clear the shadowed mctrl value at the end of suspend and restore it at the end of resume.
Fixes: 41a469482de2 ("serial: 8250: Add new 8250-core based Broadcom STB driver") Acked-by: Florian Fainelli f.fainelli@gmail.com Signed-off-by: Al Cooper alcooperx@gmail.com Link: https://lore.kernel.org/r/20211201201402.47446-1-alcooperx@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/tty/serial/8250/8250_bcm7271.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/drivers/tty/serial/8250/8250_bcm7271.c b/drivers/tty/serial/8250/8250_bcm7271.c index 7f656fac503fe..5163d60756b73 100644 --- a/drivers/tty/serial/8250/8250_bcm7271.c +++ b/drivers/tty/serial/8250/8250_bcm7271.c @@ -237,6 +237,7 @@ struct brcmuart_priv { u32 rx_err; u32 rx_timeout; u32 rx_abort; + u32 saved_mctrl; };
static struct dentry *brcmuart_debugfs_root; @@ -1133,16 +1134,27 @@ static int brcmuart_remove(struct platform_device *pdev) static int __maybe_unused brcmuart_suspend(struct device *dev) { struct brcmuart_priv *priv = dev_get_drvdata(dev); + struct uart_8250_port *up = serial8250_get_port(priv->line); + struct uart_port *port = &up->port;
serial8250_suspend_port(priv->line); clk_disable_unprepare(priv->baud_mux_clk);
+ /* + * This will prevent resume from enabling RTS before the + * baud rate has been resored. + */ + priv->saved_mctrl = port->mctrl; + port->mctrl = 0; + return 0; }
static int __maybe_unused brcmuart_resume(struct device *dev) { struct brcmuart_priv *priv = dev_get_drvdata(dev); + struct uart_8250_port *up = serial8250_get_port(priv->line); + struct uart_port *port = &up->port; int ret;
ret = clk_prepare_enable(priv->baud_mux_clk); @@ -1165,6 +1177,7 @@ static int __maybe_unused brcmuart_resume(struct device *dev) start_rx_dma(serial8250_get_port(priv->line)); } serial8250_resume_port(priv->line); + port->mctrl = priv->saved_mctrl; return 0; }