[U-Boot] A question about unconfigured pads check in omap24xx_i2c

[Heiko Schocher <hs@denx.de>]

Hello Lubomir,

Am 07.11.2013 08:57, schrieb Lubomir Popov:
> Hi Heiko,
>
> On 07-Nov-13 7:14, Heiko Schocher wrote:
>> Hello Lubomir,
>>
>> Am 06.11.2013 14:19, schrieb Lubomir Popov:
>>> On 06-Nov-13 14:12, Nikita Kiryanov wrote:
>>>> In drivers/i2c/omap24xx_i2c.c there are a few checks that attempt to
>>>> detect unconfigured pads for the i2c bus in use. These checks are
>>>> all in the form of
>>>>
>>>> if (status == I2C_STAT_XRDY) {
>>>> printf("unconfigured pads\n");
>>>> return -1;
>>>> }
>>>>
>>>> This check seems peculiar to me since the meaning of I2C_STAT_XRDY is
>>>> that new data is requested for transmission. Why is that indication that
>>>> the bus is not padconf'd for I2C?
>>> Hi Nikita,
>>>
>>> This has been empirically confirmed on OMAP4 and OMAP5. When the pads are not
>>> configured, the I2C controller is actually disconnected from the bus. The clock
>>> input for its state machine has to come from the bus however due to stretching
>>> etc., although it is internally generated. So actually nothing changes within
>>> the controller after a transaction attempt is made, and it keeps its initial
>>> state with XRDY set only (ready to accept transmit data). I use this as an
>>> indicator. Not perfect, but works in most cases.
>>
>> Thanks for this explanation! Maybe we can document this somewhere in
>> the code?
>>
>> bye,
>> Heiko
> You are right, it would be good to document it. Unfortunately I have not
> been on the U-Boot wave for some months now due to very heavy engagement
> with other stuff; have even unsubscribed from the list. I think however
> that in order to give definite statements and improve the driver, a new
> round of experiments has to be made to cover the two major types of design
> flaws (software and/or hardware): incorrect pad configuration, and missing
> pullups (internal or external). I wrote this driver more that 6 months ago
> with the goal to have something working properly (the then existing one was,
> mildly put, not good), and this detection is just a bonus side effect.
>
> In summary, the professional approach would require some more effort, which
> I'm not sure when I could afford. Otherwise, if just an explanation for the
> current algo is to be given, no problem - I can just add some comments.

I vote for the professional approach ;-) But if you have no time, and
can just send a comment for the current state (maybe with a short summary,
what should be done) I am fine with this too!

Thanks!

bye,
Heiko
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