Re: [PATCH v4 3/5] i2c: designware: Add slave definitions

[Luis Oliveira]

On 13-Dec-16 14:11, Rob Herring wrote:
> Again, please don't top post. And your line wrapping is messed up.
> IOW, you can't use Outlook.
> 
> On Tue, Dec 13, 2016 at 4:50 AM, Luis de Oliveira
> <luis.olive...@synopsys.com> wrote:
>> The controller for i2c-designware cannot be slave/master at the same time 
>> and it has to be enabled knowing beforehand if we want it to be slave or 
>> master by something outside of the controller itself.
>>
>> I as looking and I see the use of this I2C_OWN_SLAVE_ADDRESS with the 
>> "linux,slave-24c02" slave interface  but I am not seeing how it will help me 
>> identify a selected i2c-designware block as a "slave" device before 
>> instantiation. I'm sorry if I'm not understanding properly.
>> I use the "linux,slave-24c02" to instantiate the i2c-designware as a slave 
>> with an address so I can do write/read operations, it is how I tested it.
> 
> Something like this:
> 
> of_for_each_child_node(child) {
>   of_property_read_u32(child, "reg", &reg);
>   if (reg & I2C_OWN_SLAVE_ADDRESS))
>     im_a_slave = true;
> }
> 
> ...rather than testing "mode" is equal to "slave".
> 
> Rob
> 

Hi Rob, Andy,

I'm struggling to implement your suggestion @Rob. I checked the
tegra124-jetson-tk1.dts that uses that approach but I have some doubts.

My DT is as follows

        i2c@0x2000 {
                        compatible = "snps,designware-i2c";
                        reg = <0x2000 0x100>;
                        clock-frequency = <400000>;
                        clocks = <&i2cclk>;
                        interrupts = <0>;

I could add something like this:

                        eeprom@64 {
                                compatible = "linux,slave-24c02";
                                reg = <(I2C_OWN_SLAVE_ADDRESS | 0x64)>;
                        }

But I think this is different form what I was doing before. I have two 
questions:

- This way the I2C controller is identified as a slave controller or just the
subnode eeprom?
- This way looks like my slave address will be fixed

In the previous Patch v3 submission @Andy suggested a property that selects mode
that I did and it's working. And you @Rob suggested to do it a common property.
It is implemented in the DT like:

                        mode = "slave";

So before I do this changes can you please agree both if you still think this is
the best approach?


Thank you both for your time,
Luis

>>
>> Luis
>>
>> -----Original Message-----
>> From: Rob Herring [mailto:r...@kernel.org]
>> Sent: Monday, December 12, 2016 23:16
>> To: Luis de Oliveira <luis.olive...@synopsys.com>
>> Cc: w...@the-dreams.de; mark.rutl...@arm.com; jarkko.nik...@linux.intel.com; 
>> andriy.shevche...@linux.intel.com; mika.westerb...@linux.intel.com; 
>> linux-...@vger.kernel.org; devicet...@vger.kernel.org; 
>> linux-kernel@vger.kernel.org; ramiro.olive...@synopsys.com; 
>> joao.pi...@synopsys.com; carlos.palmi...@synopsys.com
>> Subject: Re: [PATCH v4 3/5] i2c: designware: Add slave definitions
>>
>> On Mon, Dec 12, 2016 at 12:35 PM, Luis de Oliveira 
>> <luis.olive...@synopsys.com> wrote:
>>> Hi all,
>>
>> Please don't top post.
>>
>>>
>>> The slave address could be set by the I2C slave backend so I can't use it 
>>> to setup the controller.
>>> A boolean property was my initial approach then Andy and Wolfram Sang 
>>> suggested the use of compatible strings and later It was suggested to use a 
>>> property to select mode but I can do it again if it's the best way.
>>> Can you please tell me where should it be documented?
>>
>> bindings/i2c/i2c.txt.
>>
>> Actually, looking at this some more, we already have a way to describe the 
>> controller being a slave device with the I2C_OWN_SLAVE_ADDRESS flag in the 
>> reg property. We should just need a helper to read reg property of each 
>> child and check for the bit set.
>>
>> Rob