From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Subject: Re: [RFC PATCH 5/5] ASoC: omap-mcbsp: Place correct
	constraints for streams
Date: Tue, 1 Jun 2010 11:07:32 +0300
Message-ID: <201006011107.32406.peter.ujfalusi@nokia.com>
References: <1275293810-31984-1-git-send-email-peter.ujfalusi@nokia.com>
	<201006010947.09640.peter.ujfalusi@nokia.com>
	<20100601103828.55e7b394.jhnikula@gmail.com>
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Cc: "tony@atomide.com" <tony@atomide.com>, "broonie@opensource.wolfsonmicro.com" <broonie@opensource.wolfsonmicro.com>, "Valentin Eduardo (Nokia-D/Helsinki)" <eduardo.valentin@nokia.com>, "Nurkkala Eero.An (EXT-Offcode/Oulu)" <ext-Eero.Nurkkala@nokia.com>, "linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>, "ext@alsa-project.org" <ext@alsa-project.org>, Girdwood <lrg@slimlogic.co.uk>
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On Tuesday 01 June 2010 10:38:28 ext Jarkko Nikula wrote:
> On Tue, 1 Jun 2010 09:47:09 +0300
> =

> Peter Ujfalusi <peter.ujfalusi@nokia.com> wrote:
> > I like the following naming:
> > omap_mcbsp_hwrule_min_buffersize()
> > omap_mcbsp_hwrule_max_periodsize()
> =

> Looks clear to me.
> =

> > Also, I think there is no point to limit the lower period size in
> > threshold mode to 32, so I will remove that as well I think.
> =

> What was the reason why period size cannot be bigger than threshold?
> This constraint was there before your patch but I don't remember reason
> for it.

When DMA is used to push the data to McBSP on OMAP3:
The McBSP threshold means, that if threshold amount of locations (words) ar=
e =

free in the buffer, than the DMA request line will be asserted, and McBSP =

expects that DMA will transfer _exactly_ threshold number of words in respo=
nse =

to the DMA request.
So, if threshold is 1 (in register it is 0), than McBSP requests for new wo=
rd, =

whenever a single location is free in the FIFO. The DMA should send 1 word =
per =

DMA request.

If threshold is configured to 100 (99 in register), than McBSP will asserts=
 the =

DMA request line, when 100 locations are free. Than DMA has to send 100 wor=
ds =

per DMA request.

So we need to limit the period size (which is used to configure the DMA's e=
lem =

count - number of words per DMA request) that it shall never be bigger than=
 the =

threshold.

> Should it be opposite that period size cannot be smaller than threshold?

No.

-- =

P=E9ter