[linux-sunxi] Re: [PATCH] ARM: dts: sun4i: Add dts file for the pov protab2-ips9 tablet

[Chen-Yu Tsai]

On Tue, Sep 8, 2015 at 3:45 PM, Hans de Goede <hdegoede at redhat.com> wrote:
> Hi,
>
> On 07-09-15 22:56, Maxime Ripard wrote:
>>
>> On Mon, Sep 07, 2015 at 09:05:29AM +0200, Hans de Goede wrote:
>>>>>
>>>>> +&reg_ldo3 {
>>>>> +       /*
>>>>> +        * We need to always power the camera sensor, otherwhise all
>>>>> access
>>>>> +        * to i2c1 is blocked.
>>>>> +        */
>>>>> +       regulator-always-on;
>>>>> +       regulator-min-microvolt = <2800000>;
>>>>> +       regulator-max-microvolt = <2800000>;
>>>>> +       regulator-name = "vdd-csi";
>>>>> +};
>>>>
>>>>
>>>> What is connected on i2c1 ? Just the camera sensor? or it has some
>>>> other devices there?
>>>
>>>
>>> The bma250 accelerometer sits there, and the kernel already has a driver
>>> for it. That driver needs to have devicetree binding support added, and
>>> then we should be able to use the accelerometer.
>>
>>
>> Ok, so if this regulator is disable, you can't access the other
>> devices as well, right?
>
>
> Right, the controller reports the bus as being stuck.
>
>> Do you know why? Is it the regulator providing
>> the pull-up voltage?
>
>
> I've tried enabling the pull ups on the SoC i2c pins, so I do not think
> that it is that, it seems that somehow when not powered the camera sensor is
> actively keeping the lines low. Either it has multiple power planes, or
> it is using normally-on fet-s between ground and its i2c lines.

FYI the reference designs use one regulator to power the pull-ups, VCC-PX
(X for X pin group), and VDDIO (IO power)on the camera sensors. AVDD, DVDD
(actual power) for the sensors are another (or more) regulators.


ChenYu