linux-kernel - Re: Re: [PATCH V5.1] serial/uart/8250: Add tunable RX interrupt trigger I/F of FIFO buffers

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Message-ID: <534F3EBC.2030606@hitachi.com>
Date:	Thu, 17 Apr 2014 11:38:52 +0900
From:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Stephen Warren <swarren@...dia.com>,
	Alan <gnomes@...rguk.ukuu.org.uk>,
	Jingoo Han <jg1.han@...sung.com>, linux-kernel@...r.kernel.org,
	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
	linux-serial@...r.kernel.org, yrl.pp-manager.tt@...achi.com,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Aaron Sierra <asierra@...-inc.com>, Jiri Slaby <jslaby@...e.cz>
Subject: Re: Re: [PATCH V5.1] serial/uart/8250: Add tunable RX interrupt
 trigger I/F of FIFO buffers

Hi Stephen,

Thank you for your reply.

(2014/04/17 2:04), Stephen Warren wrote:
> On 04/15/2014 08:08 PM, Yoshihiro YUNOMAE wrote:
>>>> diff --git a/drivers/tty/serial/8250/8250_core.c
>>>> b/drivers/tty/serial/8250/8250_core.c
>>>
>>>> @@ -2275,10 +2276,9 @@ serial8250_do_set_termios(struct uart_port
>>>> *port, struct ktermios *termios,
>>>
>>>>        if (up->capabilities & UART_CAP_FIFO && port->fifosize > 1) {
>>>> -        fcr = uart_config[port->type].fcr;
>>>> -        if ((baud < 2400 && !up->dma) || fifo_bug) {
>>>> -            fcr &= ~UART_FCR_TRIGGER_MASK;
>>>> -            fcr |= UART_FCR_TRIGGER_1;
>>>> +        /* NOTE: If fifo_bug is not set, a uaser can set RX_trigger. */
>>>> +        if ((baud < 2400 && !up->dma &&
>>>> +            (up->fcr == uart_config[port->type].fcr)) ||
>>>> up->fifo_bug) {
>>>> +            up->fcr &= ~UART_FCR_TRIGGER_MASK;
>>>> +            up->fcr |= UART_FCR_TRIGGER_1;
>>>>            }
>>>>        }
>>>
>>> Does the "(up->fcr == uart_config[port->type].fcr)" term prevent the
>>> user from changing the trigger level multiple times? Perhaps this is
>>> intended?
>>
>> No, this means that if a user changed FCR value before setting termios,
>> use the changed value because the user think changed value is always
>> set. But, I thought this is not straightforward and it cannot help
>> when the user want to use default FCR value.
>> Could I add FCR changed flag(user_changed_fcr) in uart_8250_port
>> structure and check the flag here?
>> Or shouldn't the driver check the user changing?
>
> Oh, I wasn't aware that the user could change FCR directly. To be
> honest, I'm not sure of the best way to resolve that kind of conflict...

OK. For simplicity, I don't implement the checking.
Even if FCR is changed here, users can change it any time, so this is
not so big problem, I think.

Thanks,
Yoshihiro YUNOMAE

-- 
Yoshihiro YUNOMAE
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: yoshihiro.yunomae.ez@...achi.com


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