linux-kernel - Re: [PATCH] serial: 8250_omap: Fix gpio check for auto RTS and CTS

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Date:   Sun, 6 Oct 2019 13:21:03 +0200
From:   Yegor Yefremov <yegorslists@...glemail.com>
To:     Adam Ford <aford173@...il.com>
Cc:     linux-serial@...r.kernel.org, adam.ford@...icpd.com,
        Linux-OMAP <linux-omap@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, Vignesh R <vigneshr@...com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Tony Lindgren <tony@...mide.com>,
        Douglas Anderson <dianders@...omium.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Nuno Gonçalves <nunojpg@...il.com>,
        Giulio Benetti <giulio.benetti@...ettiengineering.com>,
        Stefan Roese <sr@...x.de>
Subject: Re: [PATCH] serial: 8250_omap: Fix gpio check for auto RTS and CTS

Hi Adam,

On Sun, Oct 6, 2019 at 4:33 AM Adam Ford <aford173@...il.com> wrote:
>
> There are two checks to see if the manual gpio is configured, but
> these the check is seeing if the structure is NULL instead it
> should check to see if there are CTS and/or RTS pins defined.
>
> This patch uses checks for those individual pins instead of
> checking for the structure itself.
>
> Signed-off-by: Adam Ford <aford173@...il.com>
>
> diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
> index c68e2b3a1634..836e736ae188 100644
> --- a/drivers/tty/serial/8250/8250_omap.c
> +++ b/drivers/tty/serial/8250/8250_omap.c
> @@ -141,7 +141,7 @@ static void omap8250_set_mctrl(struct uart_port *port, unsigned int mctrl)
>
>         serial8250_do_set_mctrl(port, mctrl);
>
> -       if (!up->gpios) {
> +       if (!mctrl_gpio_to_gpiod(up->gpios, UART_GPIO_RTS)) {
>                 /*
>                  * Turn off autoRTS if RTS is lowered and restore autoRTS
>                  * setting if RTS is raised
> @@ -456,7 +456,8 @@ static void omap_8250_set_termios(struct uart_port *port,
>         up->port.status &= ~(UPSTAT_AUTOCTS | UPSTAT_AUTORTS | UPSTAT_AUTOXOFF);
>
>         if (termios->c_cflag & CRTSCTS && up->port.flags & UPF_HARD_FLOW &&
> -           !up->gpios) {
> +           !mctrl_gpio_to_gpiod(up->gpios, UART_GPIO_RTS) &&
> +           !mctrl_gpio_to_gpiod(up->gpios, UART_GPIO_CTS)) {
>                 /* Enable AUTOCTS (autoRTS is enabled when RTS is raised) */
>                 up->port.status |= UPSTAT_AUTOCTS | UPSTAT_AUTORTS;
>                 priv->efr |= UART_EFR_CTS;

Looks good to me but !up->gpios must remain as otherwise, we will get
NULL pointer dereference. What do you think?

Also adding some more people who can be interested in testing this approach.

Cheers,
Yegor