Re: [PATCH] media: i2c: OV5647: gate clock lane before stream on

[Jacob Chen]

Hi Luis,

2017-08-07 22:48 GMT+08:00 Luis Oliveira <Luis.Oliveira@xxxxxxxxxxxx>:
> Hi all,
>
> I'm new here, I got to be Maintainer of this driver by the old Maintainer
> recommendation. Still getting the hang of it :)
>
> On 07-Aug-17 13:26, Philipp Zabel wrote:
>> Hi Jacob,
>>
>> On Mon, 2017-08-07 at 19:06 +0800, Jacob Chen wrote:
>> [...]
>>>>>> --- a/drivers/media/i2c/ov5647.c
>>>>>> +++ b/drivers/media/i2c/ov5647.c
>>>>>> @@ -253,6 +253,10 @@ static int ov5647_stream_on(struct v4l2_subdev *sd)
>>>>>>  {
>>>>>>         int ret;
>>>>>>
>>>>>> +       ret = ov5647_write(sd, 0x4800, 0x04);
>>>>>> +       if (ret < 0)
>>>>>> +               return ret;
>>>>>> +
>>
>> So this clears BIT(1) (force clock lane to low power mode) and BIT(5)
>> (gate clock lane while idle) that were set by ov5647_stream_off() during
>> __sensor_init() due to the change below.
>>
>> Is there a reason, btw, that this driver is full of magic register
>> addresses and values? A few #defines would make this a lot more
>> readable.
>>
>
> For what I can see I agree that a few register name setting could be done.
>
>>>>>>         ret = ov5647_write(sd, 0x4202, 0x00);
>>>>>>         if (ret < 0)
>>>>>>                 return ret;
>>>>>> @@ -264,6 +268,10 @@ static int ov5647_stream_off(struct v4l2_subdev *sd)
>>>>>>  {
>>>>>>         int ret;
>>>>>>
>>>>>> +       ret = ov5647_write(sd, 0x4800, 0x25);
>>>>>> +       if (ret < 0)
>>>>>> +               return ret;
>>>>>> +
>>>>>>         ret = ov5647_write(sd, 0x4202, 0x0f);
>>>>>>         if (ret < 0)
>>>>>>                 return ret;
>>>>>> @@ -320,7 +328,7 @@ static int __sensor_init(struct v4l2_subdev *sd)
>>>>>>                         return ret;
>>>>>>         }
>>>>>>
>>>>>> -       return ov5647_write(sd, 0x4800, 0x04);
>>>>>> +       return ov5647_stream_off(sd);
>>
>> I see now that BIT(2) (keep bus in LP-11 while idle) is and was always
>> set. So the change is that initially, additionally to LP-11 mode, the
>> clock lane is gated and forced into low power mode, as well?
>>
>
> This is my interpretation as well.
>
>>>>>>  }
>>>>>>
>>>>>>  static int ov5647_sensor_power(struct v4l2_subdev *sd, int on)
>>>>>> --
>>>>>> 2.7.4
>>>>>>
>>>>>
>>>>> Can anyone comment on it?
>>>>>
>>>>> I saw there is a same discussion in  https://urldefense.proofpoint.com/v2/url?u=https-3A__patchwork.kernel.org_patch_9569031_&d=DwICaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=eMn12aiiNuIDjtRi5xEzC7tWJkpra2vl_XYFVvfxIGE&m=eortcRXje2uLyZNI_-Uw3Ur_z24tb-e4pZfom7WhdE0&s=6sLc76bhjR0IdaA3ArZ7F7slgtcyGz8pDTzAF_CBLno&e=
>>>>> There is a comment in i.MX CSI2 driver.
>>>>> "
>>>>> Configure MIPI Camera Sensor to put all Tx lanes in LP-11 state.
>>>>> This must be carried out by the MIPI sensor's s_power(ON) subdev
>>>>> op.
>>>>> "
>>>>> That's what this patch do, sensor driver should make sure that clock
>>>>> lanes are in stop state while not streaming.
>>>>
>>>> This is not the same, as far as I can tell. BIT(5) is just clock lane
>>>> gating, as you describe above. To put the bus into LP-11 state, BIT(2)
>>>> needs to be set.
>>>>
>>>
>>> Yeah, but i double that clock lane is not in LP11 when continue clock
>>> mode is enabled.
>
> I think by spec it shouldn't got to stopstate in continuous clock.
>
>>
>> If indeed LP-11 state is not achieved while the sensor is idle, as long
>> as BIT(5) is cleared, I think this patch is correct.
>>
>> regards
>> Philipp
>>
>
> As far as I understand, bit[5] set to 1 will force clock lane to be gated (in
> other words it will be forced to be in LP-11 if there are no packets to
> transmit). But also LP-11 must not be achieved with the BIT(5) cleared (free
> running mode)?
>

Yes. When the BIT(5) is cleared, clock lane will be in continuous mode
immediately,
unless BIT(0) is set.


> Sorry if I misunderstood something.
>
> regards,
> Luis
>