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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Mar 13, 2017 at 11:14:07AM +0000, James Hogan wrote:
> Hi Greg,
> 
> On Sat, Mar 04, 2017 at 01:09:58PM +0000, James Hogan 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.
> > 
> > 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
> 
> Any chance we could have this patch in v4.11-rc3?
> 
> As Andy pointed out, it depends on Heiko's patch:
> https://www.spinics.net/lists/linux-serial/msg25483.html

Yes, will be queueing both up soon.

thanks,

greg k-h