Re: [PATCH] serial: 8250_dw: Fix breakage when HAVE_CLK=n

[Andy Shevchenko <andy.shevchenko@gmail.com>]

On Sat, Mar 4, 2017 at 3:09 PM, James Hogan <james.hogan@imgtec.com> wrote:
> Commit 6a171b299379 ("serial: 8250_dw: Allow hardware flow control to be
> used") recently broke the 8250_dw driver on platforms which don't select
> HAVE_CLK, as dw8250_set_termios() gets confused by the behaviour of the
> fallback HAVE_CLK=n clock API in linux/clk.h which pretends everything
> is fine but returns (valid) NULL clocks and 0 HZ clock rates.
>
> That 0 rate is written into the uartclk resulting in a crash at boot,
> e.g. on Cavium Octeon III based UTM-8 we get something like this:
>
> 1180000000800.serial: ttyS0 at MMIO 0x1180000000800 (irq = 41, base_baud = 25000000) is a OCTEON
> ------------[ cut here ]------------
> WARNING: CPU: 2 PID: 1 at drivers/tty/serial/serial_core.c:441 uart_get_baud_rate+0xfc/0x1f0
> ...
> Call Trace:
> ...
> [<ffffffff8149c2e4>] uart_get_baud_rate+0xfc/0x1f0
> [<ffffffff814a5098>] serial8250_do_set_termios+0xb0/0x440
> [<ffffffff8149c710>] uart_set_options+0xe8/0x190
> [<ffffffff814a6cdc>] serial8250_console_setup+0x84/0x158
> [<ffffffff814a11ec>] univ8250_console_setup+0x54/0x70
> [<ffffffff811901a0>] register_console+0x1c8/0x418
> [<ffffffff8149f004>] uart_add_one_port+0x434/0x4b0
> [<ffffffff814a1af8>] serial8250_register_8250_port+0x2d8/0x440
> [<ffffffff814aa620>] dw8250_probe+0x388/0x5e8
> ...
>
> The clock API is defined such that NULL is a valid clock handle so it
> wouldn't be right to check explicitly for NULL. Instead treat a
> clk_round_rate() return value of 0 as an error which prevents uartclk
> being overwritten.
>

You forgot to add that it is dependent to Heiko's patch
http://www.spinics.net/lists/linux-serial/msg25314.html

Patch looks good to me and shouldn't bring any regression to Intel
hardware (x86 is using clock framework).

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>

> Fixes: 6a171b299379 ("serial: 8250_dw: Allow hardware flow control to be used")
> Signed-off-by: James Hogan <james.hogan@imgtec.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Cc: Jason Uy <jason.uy@broadcom.com>
> Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
> Cc: Heiko Stuebner <heiko@sntech.de>
> Cc: David Daney <david.daney@cavium.com>
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: linux-serial@vger.kernel.org
> Cc: linux-clk@vger.kernel.org
> Cc: linux-mips@linux-mips.org
> Cc: bcm-kernel-feedback-list@broadcom.com
> ---
>  drivers/tty/serial/8250/8250_dw.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
> index 223ac234ddb2..e65808c482f1 100644
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -267,6 +267,8 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios,
>         rate = clk_round_rate(d->clk, baud * 16);
>         if (rate < 0)
>                 ret = rate;
> +       else if (rate == 0)
> +               ret = -ENOENT;
>         else
>                 ret = clk_set_rate(d->clk, rate);
>         clk_prepare_enable(d->clk);
> --
> 2.11.1
>



-- 
With Best Regards,
Andy Shevchenko