Date: Thu, 9 May 2024 11:02:43 +0300
From: "Gjorgji Rosikopulos (Consultant)" <quic_grosikop@...cinc.com>
To: Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Jacopo Mondi
	<jacopo.mondi@...asonboard.com>
CC: Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Sakari Ailus
	<sakari.ailus@...ux.intel.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        "Paul J. Murphy" <paul.j.murphy@...el.com>,
        Martina Krasteva
	<quic_mkrastev@...cinc.com>,
        Daniele Alessandrelli
	<daniele.alessandrelli@...el.com>,
        Mauro Carvalho Chehab
	<mchehab+huawei@...nel.org>,
        <linux-media@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] media: i2c: Fix imx412 exposure control

Hi Dave,

On 5/8/2024 7:31 PM, Dave Stevenson wrote:
> Hi Jacopo and Bryan
> 
> On Wed, 8 May 2024 at 13:43, Jacopo Mondi <jacopo.mondi@...asonboard.com> wrote:
>>
>> Hi Bryan
>>
>> On Wed, May 08, 2024 at 01:30:31PM GMT, Bryan O'Donoghue wrote:
>>> On 08/05/2024 09:02, Jacopo Mondi wrote:
>>>> Hi Bryan
>>>>
>>>> On Mon, May 06, 2024 at 11:38:26PM GMT, Bryan O'Donoghue wrote:
>>>>> Currently we have the following algorithm to calculate what value should be
>>>>> written to the exposure control of imx412.
>>>>>
>>>>> lpfr = imx412->vblank + imx412->cur_mode->height;
>>>>> shutter = lpfr - exposure;
>>>>>
>>>>> The 'shutter' value is given to IMX412_REG_EXPOSURE_CIT however, the above
>>>>> algorithm will result in the value given to IMX412_REG_EXPOSURE_CIT
>>>>> decreasing as the requested exposure value from user-space goes up.
>>>>>
>>>>> e.g.
>>>>> [ 2255.713989] imx412 20-001a: Received exp 1608, analog gain 0
>>>>> [ 2255.714002] imx412 20-001a: Set exp 1608, analog gain 0, shutter 1938, lpfr 3546
>>>>> [ 2256.302770] imx412 20-001a: Received exp 2586, analog gain 100
>>>>> [ 2256.302800] imx412 20-001a: Set exp 2586, analog gain 100, shutter 960, lpfr 3546
>>>>> [ 2256.753755] imx412 20-001a: Received exp 3524, analog gain 110
>>>>> [ 2256.753772] imx412 20-001a: Set exp 3524, analog gain 110, shutter 22, lpfr 3546
>>>>>
>>>>> This behaviour results in the image having less exposure as the requested
>>>>> exposure value from user-space increases.
>>>>>
>>>>> Other sensor drivers such as ov5675, imx218, hid556 and others take the
>>>>> requested exposure value and directly.
>>>>
>>>> has the phrase been truncated or is it me reading it wrong ?
>>>
>>> Sod's law says no matter how many times you send yourself a patch before
>>> sending it to LKML you'll find a typo ~ 2 seconds after reading your patch
>>> on LKML.
>>>
>>
>> Sounds familiar enough
>>
>>>
>>>>> Looking at the range of imx sensors, it appears this particular error has
>>>>> been replicated a number of times but, I haven't so far really drilled into
>>>>> each sensor.
>>>>
>>>> Ouch, what other driver have the same issue ?
>>>
>>> So without data sheet or sensor its hard to say if these are correct or
>>> incorrect, it's the same basic calculation though.
>>>
>>> drivers/media/i2c/imx334.c::imx334_update_exp_gain()
>>>
>>>         lpfr = imx334->vblank + imx334->cur_mode->height;
>>>         shutter = lpfr - exposure;
>>>
>>>         ret = imx334_write_reg(imx334, IMX334_REG_SHUTTER, 3, shutter);
>>>
>>>
>>> drivers/media/i2c/imx335.c::imx335_update_exp_gain()
>>>
>>>         lpfr = imx335->vblank + imx335->cur_mode->height;
>>>         shutter = lpfr - exposure;
>>>
>>>         ret = imx335_write_reg(imx335, IMX334_REG_SHUTTER, 3, shutter);
>>>
>>>
>>> Looking again I'm inclined to believe the imx334/imx335 stuff is probably
>>> correct for those sensors, got copied to imx412/imx577 and misapplied to the
>>> EXPOSURE control in imx412.
>>>
>>
>> Without datasheet/devices it really is hard to tell. Cargo cult at
>> play most probably.
> 
> For reference certainly imx327/290/462 which are all siblings in the
> Sony Starvis family do calculate exposure as
> exposure = 1 frame period - (SHS1 + 1) * (1H period)
> So 0 = max exposure and bigger values are shorter exposure time.
> 
> I'm not saying that the imx412 driver is right in doing this as well,
> but it seems there is a trend with the Sony Starvis family to program
> exposure in this different manner. Don't discount it as wrong for all
> drivers!

Yes we are observing the same, the sensors which are not for mobile
market (and not have anything to do with smia leftover). The exposure
is set using the similar or the same calculation which you have posted.

~Gjorgji

> 
>   Dave
> 
>>>
>>>>> - ret = imx412_write_reg(imx412, IMX412_REG_EXPOSURE_CIT, 2, shutter);
>>>>> + ret = imx412_write_reg(imx412, IMX412_REG_EXPOSURE_CIT, 2, exposure);
>>>>
>>>> No datasheet here, can you confirm the IMX412_REG_EXPOSURE_CIT
>>>> register is actually in lines ?
>>>
>>>
>>> Looks like.
>>>
>>> From downstream "coarseIntgTimeAddr"
>>>
>>> imx577_sensor.xml
>>>     <coarseIntgTimeAddr>0x0202</coarseIntgTimeAddr>
>>>
>>> imx586/imx586_sensor.cpp
>>> pRegSettingsInfo->regSetting[regCount].registerAddr  =
>>> pExposureData->pRegInfo->coarseIntgTimeAddr + 1;
>>>
>>> pRegSettingsInfo->regSetting[regCount].registerData  = (lineCount & 0xFF);
>>>
>>>> Apart from that, as the CID_EXPOSURE control limit are correctly
>>>> updated when a new VBLANK is set by taking into account the exposure
>>>> margins, I think writing the control value to the register is the
>>>> right thing to do (if the register is in lines of course)
>>>>
>>>> Reviewed-by: Jacopo Mondi <jacopo.mondi@...asonboard.com>
>>>>
>>>> Thanks
>>>>    j
>>>>
>>>
>>> If that's good enough I'll fix the typo and apply your RB.
>>
>> Sure
>>
>> Thanks
>>   j
>>
>>>
>>> ---
>>> bod
>>>
>>
> 

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