From: andre.przywara@arm•com (Andre Przywara)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] amba-pl011: simplify TX handling
Date: Tue, 17 Mar 2015 14:55:42 +0000 [thread overview]
Message-ID: <5508406E.5060607@arm.com> (raw)
In-Reply-To: <20150317154248.1675cd4c@north>
[resent with LAKML address fixed]
Hi Jakub,
On 17/03/15 14:42, Jakub Kici?ski wrote:
> On Tue, 17 Mar 2015 13:58:44 +0000, Dave P Martin wrote:
>> On Mon, Mar 16, 2015 at 11:15:29PM +0000, Jakub Kicinski wrote:
>>> From: Jakub Kicinski <kubakici@wp•pl>
[ ... ]
>>
>> My update still keeps the softirq stuff. I wanted to avoid adding
>> status polling inside the interrupt handler's core loop, due to
>> concerns about performance overhead: without the polling, the
>> writes to DR are fire-and-forget, whereas polling FR each time
>> involves a whole round-trip to the UART which may involve significant
>> extra time cost and/or IRQ disable latency; however.
>>
>> Your approach does mitigate some of the cost by only starting to
>> poll after count chars have been transmitted, and will typically
>> halve the number of IRQs taken -- which could lead to a net benefit.
>> It would be good to see some benchmarks to understand how much
>> difference it makes to performance.
>
> I will *try* to come up with some figures but I don't have any
> high-speed UARTs so my tests run at 115k tops.
Have you tried this?
http://fw.hardijzer.nl/?p=138
This drives the RPi PL011 from a higher frequency clock, thus you can
achieve much higher baud rates. Haven't tried this myself, but it looks
reasonable and not too complicated. You need a matching speed at the
other end, of course, AFAIK the FTDI USB chip can do this.
Cheers,
Andre.
next parent reply other threads:[~2015-03-17 14:55 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1426547729-21255-1-git-send-email-moorray3@wp.pl>
[not found] ` <20150317135844.GA3759@e103592.cambridge.arm.com>
[not found] ` <20150317154248.1675cd4c@north>
2015-03-17 14:55 ` Andre Przywara [this message]
[not found] <20150317163200.GE3759@e103592.cambridge.arm.com>
2015-03-17 23:42 ` [PATCH] amba-pl011: simplify TX handling Jakub Kiciński
2015-03-18 17:41 ` Dave P Martin
2015-03-18 20:26 ` Jakub Kiciński
2015-03-18 23:43 ` Russell King - ARM Linux
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