linux-kernel - Re: [PATCH] i2c: designware: prevent early stop on TX FIFO empty

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Message-ID: <20141119141834.GJ1309@lahna.fi.intel.com>
Date:	Wed, 19 Nov 2014 16:18:34 +0200
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Wolfram Sang <wsa@...-dreams.de>
Cc:	Andrew Jackson <Andrew.Jackson@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baruch Siach <baruch@...s.co.il>,
	"Du, Wenkai" <wenkai.du@...el.com>,
	Shinya Kuribayashi <skuribay@...ox.com>,
	Romain Baeriswyl <Romain.Baeriswyl@...lis.com>,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
	Liviu Dudau <Liviu.Dudau@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] i2c: designware: prevent early stop on TX FIFO empty

On Wed, Nov 19, 2014 at 10:21:22AM +0100, Wolfram Sang wrote:
> On Fri, Nov 07, 2014 at 12:10:44PM +0000, Andrew Jackson wrote:
> > If the Designware core is configured with IC_EMPTYFIFO_HOLD_MASTER_EN
> > set to zero, allowing the TX FIFO to become empty causes a STOP
> > condition to be generated on the I2C bus. If the transmit FIFO
> > threshold is set too high, an erroneous STOP condition can be
> > generated on long transfers - particularly where the interrupt
> > latency is extended.

Makes sense to give some slack so that the interrupt handler is still
able to fill the FIFO.

> > 
> > Signed-off-by: Andrew Jackson <Andrew.Jackson@....com>
> > Signed-off-by: Liviu Dudau <Liviu.Dudau@....com>
> 
> So, what do other designware users think of this change (nice CC list
> BTW, Andrew). Adding Mika, too.

I quickly tested this on Haswell machine with touch screen connected to
the I2C bus and it still works fine, so

Tested-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
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