linux-kernel - Re: [PATCH v3 2/5] tty: Introduce SER_RS485_SOFTWARE read-only flag for struct serial

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Message-ID: <56609BBC.8010806@hurleysoftware.com>
Date:	Thu, 3 Dec 2015 14:45:00 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	"Matwey V. Kornilov" <matwey@....msu.ru>
Cc:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Greg KH <gregkh@...uxfoundation.org>, jslaby@...e.com,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH v3 2/5] tty: Introduce SER_RS485_SOFTWARE read-only flag
 for struct serial_rs485

On 12/03/2015 12:29 PM, Matwey V. Kornilov wrote:
> 2015-12-03 17:41 GMT+03:00 Peter Hurley <peter@...leysoftware.com>:
>> Hi Matwey,
>>
>> On 12/03/2015 12:50 AM, Matwey V. Kornilov wrote:
>>> I am working on v4, where I completely redesigned implementation. And
>>> now I think that it is considerably better than v3.
>>> It looks like the following:
>>> https://github.com/matwey/linux/commits/8520_rs485_v4
>>> But it is not ready yet, there is a bug somewhere.
>>>
>>> In the v4, each subdriver decides separately if it needs rs485
>>> emulation support. Then it enables it like the following:
>>> https://github.com/matwey/linux/commit/4455e425fc045713fb921ccec695fe183f1558f0
>>> Before calling serial8250_rs485_emul_enabled, the driver enables
>>> interrupt on empty shift register (they are always there for omap_).
>>
>> Looks good.
>>
>> Are you testing with CONFIG_SERIAL_8250_DMA=n first to simplify the
>> debug effort? DMA adds a completely different tx path.
> 
> Many thanks for the advice. I've just found that the bug is not in my code =)
> Even with pure 4.3.0 I cannot open /dev/ttyS5 more than once. It just
> hangs on open() and the process is in S+ state.

Hmm, that's odd. So

$ stty -a < /dev/ttyS5

hangs if something like below is running?

$ cat > /dev/ttyS5


>> Also, before submission, please shorten the identifiers. And Greg hates
>> functions returning bool so just expanded serial8250_rs485_emul_enabled()
>> inline.
> 
> Am I allowed to use `re' instead of rs485_emul in names?

Long names and constructs tend to obscure the execution flow.
Some of the names could be reduced where the meaning is obvious:

  serial8250_rts_on_send
  serial8250_rts_after_send
  serial8250_handle_start_timer
  serial8250_handle_stop_timer

These two I would inline into their lone call site:

  serial8250_rs485_emul_startup()
  serial8250_rs485_emul_shutdown()

serial8250_rs485_emul_start_tx  => __start_tx_rs485

rs485_emul => sw485/em485/emul485/soft485 ?

Or just rs485 (except for the field name and structs so as not to confuse
it with the port->rs485)

Just my 2¢

Regards,
Peter Hurley


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