linux-kernel - Re: [PATCH v4] tty: serial: men_z135_uart: Fix driver for changes in hardware

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Message-ID: <545A59F5.8000202@hurleysoftware.com>
Date:	Wed, 05 Nov 2014 12:10:13 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Johannes Thumshirn <johannes.thumshirn@....de>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] tty: serial: men_z135_uart: Fix driver for changes
 in hardware

On 11/05/2014 11:39 AM, Johannes Thumshirn wrote:
> On Mon, Nov 03, 2014 at 04:26:39PM -0500, Peter Hurley wrote:
>> On 11/03/2014 04:01 PM, Peter Hurley wrote:
>>> On 11/03/2014 11:05 AM, Johannes Thumshirn wrote:
>>>> * Enable the handling of UART core's automatic flow control feature.
>>>>   When AFE is active disable generation of modem status IRQs.
>>>
>>> So HUPCL doesn't work when CRTSCTS is set?
>>
>> Sorry, I meant !CLOCAL. IOW,
>>
>> 'So !CLOCAL doesn't work when CRTSCTS is set?'
> 
> Yes, unfortunately

Then you want to reset CLOCAL back on in the termios when
you enable auto flow control. That way, the process can see which
termios changes were successful and which were unsuccessful.
Plus, it keeps the serial core state sync'd with the driver.

Optionally, you could consider overriding CRTSCTS when !CLOCAL; iow,
if !CLOCAL, then disable CRTSCTS instead. (In that case, you would
reset CRTSCTS in the termios as well, so the process would be aware
of the changes).

>>
>>> Is this because there's actually a problem with the IP core that
>>> MSIs trash the autoCTS state, or is the problem that the driver
>>> just shouldn't be calling uart_handle_cts_change() when autoCTS is
>>> on?
>>
> 
> From our investigations it looks like it trashes the autoCTS state.

Ok.

Regards,
Peter Hurley
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