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

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