linux-kernel - Re: [PATCH] serial: don't announce CIR serial ports

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Message-ID: <55C20324.2030305@maciej.szmigiero.name>
Date:	Wed, 05 Aug 2015 14:35:48 +0200
From:	"Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:	Peter Hurley <peter@...leysoftware.com>
CC:	linux-serial@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] serial: don't announce CIR serial ports

On 05.08.2015 04:03, Peter Hurley wrote:
> On 08/04/2015 07:25 PM, Maciej S. Szmigiero wrote:
>> Hi Peter,
>>
>> Thanks for looking into it.
>>
>> On 04.08.2015 03:46, Peter Hurley wrote:
>>> Hi Maciej,
>>>
>>> On 08/02/2015 05:09 PM, Maciej S. Szmigiero wrote:
>>>> CIR type serial ports aren't real serial ports.
>>>> This is just a way to prevent legacy serial driver
>>>> from probing and eventually binding some resources
>>>> so don't announce them like normal serial ports.
>>>
>>> I'd like to keep some form of reporting so that we know the
>>> port was properly probed; what about extending uart_report_port()
>>> to including CIR + disabled status?
>>
>> Currently the printed message looks like this:
>> "00:01: ttyS2 at I/O 0x3e8 (irq = 7, base_baud = 115200) is a CIR port".
>>
>> I think it would be best to skip a device file name in this case,
>> since this is how user sees (and uses) a real serial port.
>> The message would be then:
>> "00:01 at I/O 0x3e8 (irq = 7, base_baud = 115200) is a CIR port".
>>
>> The dev name will always be present since the only current
>> "source" of CIR ports is PNP 8250 driver which sets 
>> dev pointer uncondtionally.
>>
>>> Secondly, good catch! Because we should not be trying to
>>> register a console on this port, nor driving modem signals.
>>>
>>> So maybe an early exit after uart_report_port?
>>
>> All right, I will resubmit updated patch tomorrow.
> 
> In re-reviewing this, I think the proper solution is actually not
> to add the uart port for a CIR port at all. It doesn't make
> sense because the tty cannot be changed by setserial/ioctl(TIOCSSERIAL),
> so the device node serves no purpose.
> 
> This problem is really an artifact of the 8250 driver port management,
> and shouldn't involve the serial core at all.
> 
> An additional benefit of this approach is that a simple one-line
> banner noting the port skip could be emitted instead from
> serial8250_register_8250_port().

That's a good idea, checks for PORT_8250_CIR in serial port
callbacks can be removed too this way, since these callbacks
won't ever be called.

I've submitted an updated patch.

> Regards,
> Peter Hurley
 
Best regards,
Maciej Szmigiero

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