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

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Message-ID: <CAJs94EaLF-eYj3jao65bBGzVkrBdu8GSxmr+H=2b5J0VQNxsuQ@mail.gmail.com>
Date:	Fri, 4 Dec 2015 20:50:25 +0300
From:	"Matwey V. Kornilov" <matwey@....msu.ru>
To:	Peter Hurley <peter@...leysoftware.com>
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

2015-12-03 22:45 GMT+03:00 Peter Hurley <peter@...leysoftware.com>:
> 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
>

Nonblocking mode works, blocking mode hands on tty_port_block_til_ready
https://bugzilla.kernel.org/show_bug.cgi?id=108851

>
>>> Also, before submission, please shorten the identifiers. And Greg hates
>>> functions returning bool so just expanded serial8250_rs485_emul_enabled()
>>> inline.

I would like to keep it as API to hide implementation details.
In other words, I don't want to inline it in omap_8250_rs485_config.

>>
>> 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
>
>



-- 
With best regards,
Matwey V. Kornilov.
Sternberg Astronomical Institute, Lomonosov Moscow State University, Russia
119991, Moscow, Universitetsky pr-k 13, +7 (495) 9392382
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