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

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Message-ID: <524EC4B9.7000202@monstr.eu>
Date:	Fri, 04 Oct 2013 15:38:01 +0200
From:	Michal Simek <monstr@...str.eu>
To:	Lars-Peter Clausen <lars@...afoo.de>
CC:	Wolfram Sang <wsa@...-dreams.de>,
	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>,
	"Steven A. Falco" <sfalco@...ris.com>
Subject: Re: [PATCH v2 2/3] i2c: xilinx: Set tx direction in write operation

On 10/04/2013 03:38 PM, Lars-Peter Clausen wrote:
> On 10/04/2013 03:09 PM, Michal Simek wrote:
>>
>>
>> On 10/04/2013 02:12 PM, Lars-Peter Clausen wrote:
>>> On 10/04/2013 01:55 PM, Wolfram Sang wrote:
>>>> 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
>>>
>>> The current version works fine here. The driver uses whats described in the
>>> datasheet as "dynamic controller logic flow" and not the "standard
>>> controller logic flow". The sequence Michal mentioned above is from the
>>> "standard controller logic flow" section.
>>
>> Does this change break "dynamic controller logic flow"?
> 
> Not sure, but I would assume that the bit is ignored in this mode. But I
> don't think the patch should be applied since this step is not in the
> sequence of steps that should be done.

Kedar: Can you please look at both these modes and provide feedback?

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/
Maintainer of Linux kernel - Xilinx Zynq ARM architecture
Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform



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