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

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Message-ID: <20141119133531.GD2374@sapphire.tkos.co.il>
Date:	Wed, 19 Nov 2014 15:35:32 +0200
From:	Baruch Siach <baruch@...s.co.il>
To:	Wolfram Sang <wsa@...-dreams.de>
Cc:	Andrew Jackson <Andrew.Jackson@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"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>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH] i2c: designware: prevent early stop on TX FIFO empty

Hi Wolfram,

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.
> > 
> > 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 don't have access to this hardware anymore so I can't test. As far as I 
remember the spec this change should be OK.

baruch

> >  drivers/i2c/busses/i2c-designware-core.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
> > index 3c20e4b..e070edd 100644
> > --- a/drivers/i2c/busses/i2c-designware-core.c
> > +++ b/drivers/i2c/busses/i2c-designware-core.c
> > @@ -363,7 +363,7 @@ int i2c_dw_init(struct dw_i2c_dev *dev)
> >  	}
> >  
> >  	/* Configure Tx/Rx FIFO threshold levels */
> > -	dw_writel(dev, dev->tx_fifo_depth - 1, DW_IC_TX_TL);
> > +	dw_writel(dev, dev->tx_fifo_depth / 2, DW_IC_TX_TL);
> >  	dw_writel(dev, 0, DW_IC_RX_TL);
> >  
> >  	/* configure the i2c master */

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