linux-kernel - Re: Clock framework deadlock with external SPI clockchip

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Message-ID: <20130904100606.GU3084@sirena.org.uk>
Date:	Wed, 4 Sep 2013 11:06:06 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Mike Turquette <mturquette@...aro.org>
Cc:	Lars-Peter Clausen <lars@...afoo.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Hennerich, Michael" <Michael.Hennerich@...log.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Clock framework deadlock with external SPI clockchip

On Tue, Sep 03, 2013 at 04:22:29PM -0700, Mike Turquette wrote:
> Quoting Lars-Peter Clausen (2013-08-30 06:24:45)

> > === Clock chip driver ===        === SPI master driver ===
> >  clk_prepare_lock()
> >  spi_sync()
> >    wait_for_completion(X)

> Is there a synchronous equivalent to spi_sync()?

spi_sync() is synchronous?  Obviously everything is asynchronous up to
that point but the only way the driver can tell if the I/O completed is
using spi_sync() or the equivalent thereof.

If you're asking if there is a way of doing SPI I/O that isn't multi
threaded then there isn't, in order to keep pushing transfers into the
SPI controller to saturate the bus we have a high priority task to push
more data in.  SPI buses can be quite high bandwidth in some
applications.

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