[PATCH] i2c: designware: prevent early stop on TX FIFO empty

[PATCH] i2c: designware: prevent early stop on TX FIFO empty

[Andrew Jackson]

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@arm.com>
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
---
 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 */
-- 
1.7.1

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

[Wolfram Sang]

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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@arm.com>
> Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>

So, what do other designware users think of this change (nice CC list
BTW, Andrew). Adding Mika, too.

> ---
>  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 */
> -- 
> 1.7.1
> 

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

[Baruch Siach]

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@arm.com>
> > Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.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 */

-- 
     http://baruch.siach.name/blog/                  ~. .~   Tk Open Systems
=}------------------------------------------------ooO--U--Ooo------------{=
   - baruch@tkos.co.il - tel: +972.2.679.5364, http://www.tkos.co.il -

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

[Mika Westerberg]

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@arm.com>
> > Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.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@linux.intel.com>

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

[Wolfram Sang]

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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@arm.com>
> Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>

Applied to for-current, thanks!


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