linux-kernel - Re: [PATCH] tty: serial: msm

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Message-Id: <20190520145110.7BDAE21721@mail.kernel.org>
Date:   Mon, 20 May 2019 07:51:09 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     agross@...nel.org, david.brown@...aro.org,
        gregkh@...uxfoundation.org, jorge.ramirez-ortiz@...aro.org
Cc:     jslaby@...e.com, keescook@...omium.org, anton@...msg.org,
        ccross@...roid.com, tony.luck@...el.com,
        linux-arm-msm@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, khasim.mohammed@...aro.org,
        agsumit@....qualcomm.com
Subject: Re: [PATCH] tty: serial: msm_serial: Fix XON/XOFF

Quoting Jorge Ramirez-Ortiz (2019-05-20 03:34:35)
> When the tty layer requests the uart to throttle, the current code
> executing in msm_serial will trigger "Bad mode in Error Handler" and
> generate an invalid stack frame in pstore before rebooting (that is if
> pstore is indeed configured: otherwise the user shall just notice a
> reboot with no further information dumped to the console).
> 
> This patch replaces the PIO byte accessor with the word accessor
> already used in PIO mode.

Because the hardware only accepts word based accessors and fails
otherwise? I can believe that.

I wonder if the earlier UART hardware this driver used to support (i.e.
pre-DM) would accept byte access to the registers. It's possible, but we
don't really care because those boards aren't supported.

> 
> Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@...aro.org>
> ---

Reviewed-by: Stephen Boyd <swboyd@...omium.org>

>  drivers/tty/serial/msm_serial.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
> index 109096033bb1..23833ad952ba 100644
> --- a/drivers/tty/serial/msm_serial.c
> +++ b/drivers/tty/serial/msm_serial.c
> @@ -869,10 +870,12 @@ static void msm_handle_tx(struct uart_port *port)
>                 else
>                         tf = port->membase + UART_TF;
>  
> +               buf[0] = port->x_char;
> +
>                 if (msm_port->is_uartdm)
>                         msm_reset_dm_count(port, 1);
>  
> -               iowrite8_rep(tf, &port->x_char, 1);
> +               iowrite32_rep(tf, buf, 1);

I suppose it's OK to write some extra zeroes here?