linux-kernel - Re: [PATCH 1/4] hvc_console: do not set low

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Date:	Thu, 8 Jan 2009 07:25:14 -0600
From:	Milton Miller <miltonm@....com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Christian Borntraeger <borntraeger@...ibm.com>,
	Benjiman Herrenschmidt <benh@...nel.crashing.org>,
	linuxppc-dev list <linuxppc-dev@...abs.org>,
	Joe Peterson <joe@...rush.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] hvc_console: do not set low_latency


On Jan 8, 2009, at 6:36 AM, Alan Cox wrote:

>> v2.6.16-rc1 via 33f0f88f1c51ae5c2d593d26960c760ea154c2e2
>>     [PATCH] TTY layer buffering revamp
>>
>> added this new api.
>
> No - tty_flip_buffer_push is from 2.1.66 and with the same constraints
> from the day it was added.
>
Yes but wrappers were added and this this and many ohter drivers were  
converted to use them:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git; 
a=commitdiff;h=33f0f88f1c51ae5c2d593d26960c760ea154c2e2

And they were slightly buggy leading to the buggy workaround.

>
>> Having the flag set for purely polled drivers will save delaying
>> the work when receiving input for 1 jiffie.
>>
>>
>> Index: work.git/drivers/char/hvc_console.c
>> ===================================================================
>> --- work.git.orig/drivers/char/hvc_console.c	2009-01-08  
>> 03:01:24.000000000 -0600
>> +++ work.git/drivers/char/hvc_console.c	2009-01-08 03:01:51.000000000  
>> -0600
>> @@ -318,7 +318,8 @@ static int hvc_open(struct tty_struct *t
>>  	} /* else count == 0 */
>>
>>  	tty->driver_data = hp;
>> -	tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */
>> +	if (!hp->irq_requested)
>> +		tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */
>>
>>  	hp->tty = tty;
>
> Looks good to me

Thanks, I guess that is an Ack?

milton

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