linux-kernel - Re: [RESEND RFC PATCH 1/3] ASoC: mediatek: Add binding support for AFE driver

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Message-ID: <20150420043747.GH6325@pengutronix.de>
Date:	Mon, 20 Apr 2015 06:37:47 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Mark Brown <broonie@...nel.org>
Cc:	Koro Chen <koro.chen@...iatek.com>, robh+dt@...nel.org,
	matthias.bgg@...il.com, perex@...ex.cz, tiwai@...e.de,
	srv_heupstream@...iatek.com, linux-mediatek@...ts.infradead.org,
	galak@...eaurora.org, lgirdwood@...il.com,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, alsa-devel@...a-project.org
Subject: Re: [RESEND RFC PATCH 1/3] ASoC: mediatek: Add binding support for
 AFE driver

On Sat, Apr 18, 2015 at 06:34:07PM +0100, Mark Brown wrote:
> On Fri, Apr 10, 2015 at 04:14:07PM +0800, Koro Chen wrote:
> 
> > +Each external interface (called "IO" in this driver) is presented as a
> > +DAI to ASoC. An IO must be connected via the interconnect to a memif.
> > +The connection paths are configured through the device tree.
> 
> Why are these connection paths configured via device tree?  I would
> expect that either there would be runtime configurability of these
> things (particularly if loopback configurations within the hardware are
> possible) or we'd just allocate memory interfaces to DAIs automatically
> as DAIs come into use.

There is a crossbar switch between the memory interfaces and the DAIs.
Not every connection is possible, so not every memory interface can be
used for every DAI. An algorithm choosing a suitable memory interface
must be quite clever, complicated and also SoC dependent (the same but
different hardware is used on MT8135 aswell), so I thought offering a
static configuration via device tree is a good start. Should there be
runtime configuration possible later the device tree settings could
provide a good default.

> 
> > +- mem-interface-playback:
> > +  mem-interface-capture: property of memif, format is: <memif irq use_sram>;
> > +	                 memif: which memif to be used
> > +			        (defined in include/dt-bindings/sound/mtk-afe.h)
> > +		         irq: which irq to be used
> > +			      (defined in include/dt-bindings/sound/mtk-afe.h)
> > +		         use_sram: 1 is yes, 0 is no
> 
> Again, this looks like stuff we should be able to figure out at runtime
> - the use of SRAM in particular looks like something we might want to
> change depending on use case.  Assuming it adds buffering then for a
> VoIP application we might not want to use SRAM to minimize latency but
> during music playback we might want to enable SRAM to minimize power
> consumption.

That's exactly the usecase. How could such a runtime configurability
look like? sysfs? Or something based on the buffer sizes?

Sascha

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