From: Peter Ujfalusi <peter.ujfalusi@ti.com>
To: Mark Brown <broonie@kernel.org>, Greg Knight <g.knight@symetrica.com>
Cc: linux-spi@vger.kernel.org,
"linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>
Subject: Re: Patch to parameterize DMA_MIN_BYTES for omap2-mcspi
Date: Fri, 20 Mar 2015 15:10:04 +0200 [thread overview]
Message-ID: <550C1C2C.5080204@ti.com> (raw)
In-Reply-To: <20150319185129.GZ2869@sirena.org.uk>
On 03/19/2015 08:51 PM, Mark Brown wrote:
> On Thu, Mar 19, 2015 at 01:28:00PM -0400, Greg Knight wrote:
>
>> Changing DMA_MIN_BYTES to, say, "dma_min_time_ms" sounds reasonable to
>> me. I don't know how to compute it completely accurately as some SPI
>
> You probably need both - there's often a hard limit where the FIFO size
> in the hardware becomes a limit for DMA as well as a soft limit on top
> of that for performance reasons.
The FIFO is only going to be enabled when the DMA is used for transfer so we
should have some lower limit for the PIO/DMA threshold. The FIFO in McSPI is a
tricky one anyways, since it has only one FIFO but several channels and the
FIFO can be enabled for only one channel, if it is enabled for more channels
it is not going to be used by either channel.
--
Péter
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next prev parent reply other threads:[~2015-03-20 13:10 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-19 5:05 Patch to parameterize DMA_MIN_BYTES for omap2-mcspi Greg Knight
2015-03-19 9:47 ` Mark Brown
2015-03-19 12:34 ` Peter Ujfalusi
2015-03-19 13:16 ` Greg Knight
[not found] ` <CAAQQ3un3k-0nY8xaOXKbmCznOk69ZEhbWLd5ZZV1_=rQLOyspg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-03-19 14:03 ` Mark Brown
2015-03-19 16:23 ` Peter Ujfalusi
[not found] ` <550AF7F6.7080200-l0cyMroinI0@public.gmane.org>
2015-03-19 17:28 ` Greg Knight
2015-03-19 18:51 ` Mark Brown
2015-03-20 13:10 ` Peter Ujfalusi [this message]
[not found] ` <550C1C2C.5080204-l0cyMroinI0@public.gmane.org>
2015-03-22 16:31 ` Mark Brown
2015-03-20 12:58 ` Peter Ujfalusi
-- strict thread matches above, loose matches on Subject: below --
2015-03-18 19:37 Greg Knight
2015-03-18 20:31 ` Tony Lindgren
[not found] ` <CAAQQ3umQu=Zh6MC=uXTxzbXGgm48KY6KQTPo4=f=0cVy+FFv-Q@mail.gmail.com>
2015-03-18 22:01 ` Tony Lindgren
2015-03-18 22:04 ` Greg Knight
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