Re: [PATCH] i2c: omap: fix bus recovery setup

From: Grygorii Strashko <grygorii.strashko-l0cyMroinI0@public.gmane.org>
To: Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>,
	Jan Luebbe <jlu-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
Cc: Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>,
	Felipe Balbi <balbi-l0cyMroinI0@public.gmane.org>,
	linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
	kernel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org
Subject: Re: [PATCH] i2c: omap: fix bus recovery setup
Date: Tue, 14 Jul 2015 15:10:01 +0300	[thread overview]
Message-ID: <55A4FC19.4040709@ti.com> (raw)
In-Reply-To: <20150714111004.GB1517@katana>

Hi Wolfram,

On 07/14/2015 02:10 PM, Wolfram Sang wrote:
> On Wed, Jul 08, 2015 at 04:35:27PM +0200, Jan Luebbe wrote:
>> At least on the AM335x, enabling OMAP_I2C_SYSTEST_ST_EN is not enough to
> 
> Felipe: it seems you did not need this; is this AM335x specific?

We need it (Felipe's reply can be delayed).

It's not AM335x specific. TMODE has to be configured for all OMAP4+ SoCs too.

> 
>> allow direct access to the SCL and SDA pins. In addition to ST_EN, we
>> need to set the TMODE to 0b11 (Loop back & SDA/SCL IO mode select).
>> Also, as the reset values of SCL_O and SDA_O are 0 (which means "drive
>> low level"), we need to set them to 1 (which means "high-impedance") to
>> avoid unwanted changes on the pins.
>>
>> As a precaution, reset all these bits to their default values after
>> recovery is complete.

Reviewed-by: Grygorii Strashko <grygorii.strashko-l0cyMroinI0@public.gmane.org> 

>>
>> Signed-off-by: Jan Luebbe <jlu-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
>> ---
>>   drivers/i2c/busses/i2c-omap.c | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
>> index d1c22e3fdd14..fc9bf7f30e35 100644
>> --- a/drivers/i2c/busses/i2c-omap.c
>> +++ b/drivers/i2c/busses/i2c-omap.c
>> @@ -1247,7 +1247,14 @@ static void omap_i2c_prepare_recovery(struct i2c_adapter *adap)
>>   	u32 reg;
>>   
>>   	reg = omap_i2c_read_reg(dev, OMAP_I2C_SYSTEST_REG);
>> +	/* enable test mode */
>>   	reg |= OMAP_I2C_SYSTEST_ST_EN;
>> +	/* select SDA/SCL IO mode */
>> +	reg |= 3 << OMAP_I2C_SYSTEST_TMODE_SHIFT;
>> +	/* set SCL to high-impedance state (reset value is 0) */
>> +	reg |= OMAP_I2C_SYSTEST_SCL_O;
>> +	/* set SDA to high-impedance state (reset value is 0) */
>> +	reg |= OMAP_I2C_SYSTEST_SDA_O;
>>   	omap_i2c_write_reg(dev, OMAP_I2C_SYSTEST_REG, reg);
>>   }
>>   
>> @@ -1257,7 +1264,11 @@ static void omap_i2c_unprepare_recovery(struct i2c_adapter *adap)
>>   	u32 reg;
>>   
>>   	reg = omap_i2c_read_reg(dev, OMAP_I2C_SYSTEST_REG);
>> +	/* restore reset values */
>>   	reg &= ~OMAP_I2C_SYSTEST_ST_EN;
>> +	reg &= ~OMAP_I2C_SYSTEST_TMODE_MASK;
>> +	reg &= ~OMAP_I2C_SYSTEST_SCL_O;
>> +	reg &= ~OMAP_I2C_SYSTEST_SDA_O;
>>   	omap_i2c_write_reg(dev, OMAP_I2C_SYSTEST_REG, reg);
>>   }
>>   
>> -- 
>> 2.1.4
>>

-- 
regards,
-grygorii