Hi Doug,
On 03.09.2015 02:19, Doug Anderson wrote:
> Russell,
>
> On Wed, Sep 2, 2015 at 4:04 PM, Russell King - ARM Linux
> <linux@xxxxxxxxxxxxxxxx> wrote:
>>>> Also, is it appropriate to hook non-DDC devices to a DDC bus? I suspect
>>>> that's asking for trouble.
>>>
>>> I doubt it's appropriate. Why do you ask?
>>
>> To find out why you want to "specify the I2C bus".
>>
>> Surely if we're talking about the DDC bus, we either want to use a
>> separate I2C bus (in which case the HDMI DT description needs to
>> specify which I2C bus to use) or we want to use the HDMI-internal
>> I2C bus, which being part of the HDMI driver, the HDMI driver will
>> know how to find it itself - there should be no need to put an
>> explicit ddc-i2c-bus self-reference there in that case.
>
> Overall it comes down to bus numbering. Possibly that's a stupid
> reason, but it is my reason nevertheless.
this is a known issue regarding I2C bus numbering.
> Specifically it significantly helps my brain process kernel log
> messages if the i2c bus that's referred to "bus 5" in my SoC's user
> manual shows up consistently as "i2c5" in kernel log messages. It's
> helpful it it shows up as "i2c5" even if "i2c0" - "i2c4" aren't
> enabled.
>
> That's all totally possible by using this type of syntax, like in rk3288.dtsi:
>
> aliases {
> i2c0 = &i2c0;
> i2c1 = &i2c1;
> i2c2 = &i2c2;
> i2c3 = &i2c3;
> i2c4 = &i2c4;
> i2c5 = &i2c5;
>
> Similarly, I'd like "bus 0" to show up as i2c0, which will happen as
> you can see in the above.
>
> The problem is that if another bus registers itself before the SoC's
> i2c0 registers itself and that bus doesn't give a number to itself
> then the i2c subsystem will chose "I2C 0". ...and then when the main
> SoC i2c bus registers itself it will fail because i2c0 is already
> taken.
>
> By having a of_node for the hdmi i2c bus, we can assign a number to it like:
> i2c15 = &hdmi;
>
> This is all described in the two links I referenced in my original reply.
>
>
> A possible other option is to have the i2c subsystem try to start
> numbering at a larger base for all automatically numbered busses
> (those that didn't specify a number). Then it's more likely (though
> still not guaranteed) to conflict with another bus...
Could you please check if commit 03bde7c31a3 serves you?
--
With best wishes,
Vladimir
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