Re: [PATCH 04/18] Blackfin Serial Driver: Change hardware flowcontrol from poll to interrupt driven.

Mike Frysinger
2009-03-06T22:49:26Z

On Fri, Mar 6, 2009 at 17:38, Andrew Morton wrote:
> On Fri,  6 Mar 2009 14:42:46 +0800 Bryan Wu wrote:
>> From: Sonic Zhang <sonic.zhang@analog.com>
>>
>> Only CTS bit is affected.
>>
>> Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
>> Signed-off-by: Bryan Wu <cooloney@kernel.org>
>
> Another completely useless changelog.

the summary, while brief, describes the change: the flowcontrol is
currently implemented by polling, but this changes it to an interrupt
based system

> Your [PATCH 00/18] email described all these patches as
> needed-in-2.6.29 bugfixes.  As far as I can tell (based on almost zero
> information), this patch is not a bugfix.

because the current implementation is polling (busy waiting), the
kernel will basically hang when the remote asserts hardware
flowcontrol pins. if this is only asserted for short periods (less
than 1 char time), then it's not really noticed ... but it still
destroys latencies.
-mike