linux-kernel - Re: [PATCH v2 1/1] serial: 8250_dw: Allow hardware flow control to be used

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Date:   Wed, 01 Mar 2017 20:50:20 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     James Hogan <james.hogan@...tec.com>,
        Jason Uy <jason.uy@...adcom.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Noam Camus <noamc@...hip.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Wang Hongcheng <annie.wang@....com>,
        linux-serial@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        bcm-kernel-feedback-list@...adcom.com,
        Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
        David Daney <david.daney@...ium.com>
Subject: Re: [PATCH v2 1/1] serial: 8250_dw: Allow hardware flow control to
 be used

On Wed, 2017-03-01 at 18:02 +0000, James Hogan wrote:
> On 11 January 2017 at 19:48, Jason Uy <jason.uy@...adcom.com> wrote:
> > In the most common use case, the Synopsys DW UART driver does not
> > set the set_termios callback function.  This prevents UPSTAT_AUTOCTS
> > from being set when the UART flag CRTSCTS is set.  As a result, the
> > driver will use software flow control as opposed to hardware flow
> > control.
> > 
> > To fix the problem, the set_termios callback function is set to the
> > DW specific function.  The logic to set UPSTAT_AUTOCTS is moved so
> > that any clock error will not affect setting the hardware flow
> > control.

> Bisection shows that this patch, commit
> 6a171b29937984a5e0bf29d6577b055998f03edb, has broken boot of the
> Cavium Octeon III based UTM-8 board (MIPS architecture).
> 
> I now get the following warning:

> [<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

> Then it hangs and the watchdog restarts the machine.
> 
> Any ideas?

1. Does it use clock on that platform?
2. Check if termios is not NULL there.

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy