linux-kernel - Re: [PATCH v2 2/3] i2c: xilinx: Set tx direction in write operation

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Date:	Fri, 4 Oct 2013 13:55:17 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Michal Simek <monstr@...str.eu>
Cc:	Michal Simek <michal.simek@...inx.com>,
	linux-kernel@...r.kernel.org,
	Kedareswara rao Appana <appana.durga.rao@...inx.com>,
	Kedareswara rao Appana <appanad@...inx.com>,
	Jean Delvare <khali@...ux-fr.org>,
	Peter Korsgaard <jacmet@...site.dk>, linux-i2c@...r.kernel.org,
	Richard Röjfors 
	<richard.rojfors@...agicore.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	"Steven A. Falco" <sfalco@...ris.com>
Subject: Re: [PATCH v2 2/3] i2c: xilinx: Set tx direction in write operation

On Fri, Oct 04, 2013 at 11:53:49AM +0200, Michal Simek wrote:
> On 10/04/2013 07:46 AM, Wolfram Sang wrote:
> > 
> >> +	cr = xiic_getreg32(i2c, XIIC_CR_REG_OFFSET);
> >> +	cr |= XIIC_CR_DIR_IS_TX_MASK;
> >> +	xiic_setreg32(i2c, XIIC_CR_REG_OFFSET, cr);
> >> +
> > 
> > Is there no need to clear the bit again when receiving?
> 
> This bit is cleared in xiic_xfer() -> xiic_start_xfer() ->xiic_reinit()
> 
> xiic_setreg8(i2c, XIIC_CR_REG_OFFSET, XIIC_CR_TX_FIFO_RESET_MASK);

A bit implicit, but OK.

> > And did
> > transferring ever work if this bit was never set before?
> 
> I really don't know. We have switched from old driver to this new mainline one
> and based on our eeprom testing we have found that this bit hasn't been setup properly.
> 
> It is described here.
> http://www.xilinx.com/support/documentation/ip_documentation/axi_iic/v1_02_a/axi_iic_ds756.pdf
> page 28 - step 3.
> 
> IIC Master Transmitter with a Repeated Start
> 1. Write the IIC device address to the TX_FIFO.
> 2. Write data to TX_FIFO.
> 3. Write to Control Register (CR) to set MSMS = 1 and TX = 1.
> 4. Continue writing data to TX_FIFO.
> 5. Wait for transmit FIFO empty interrupt. This implies the IIC has throttled the bus.
> 6. Write to CR to set RSTA = 1.

Repeated start is not happening in the driver as well, or am I
overlooking something?

> 7. Write IIC device address to TX_FIFO.
> 8. Write all data except last byte to TX_FIFO.
> 9. Wait for transmit FIFO empty interrupt. This implies the IIC has throttled the bus.
> 10. Write to CR to set MSMS = 0. The IIC generates a stop condition at the end of the last byte.
> 11. Write last byte of data to TX_FIFO.

CCing more people who worked on the driver in the past and might have
experiences

Thanks,

   Wolfram


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