linux-kernel - Re: [PATCH v2 1/5] media: i2c: imx335: Drop setting of 0x3a00 register

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Date: Wed, 7 Feb 2024 09:51:32 +0530
From: Umang Jain <umang.jain@...asonboard.com>
To: Matthias Fend <matthias.fend@...end.at>,
 Kieran Bingham <kieran.bingham@...asonboard.com>, linux-media@...r.kernel.org
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
 open list <linux-kernel@...r.kernel.org>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>
Subject: Re: [PATCH v2 1/5] media: i2c: imx335: Drop setting of 0x3a00
 register

Hi,

On 1/31/24 4:02 PM, Matthias Fend wrote:
> Hi Kieran,
>
> Am 31.01.2024 um 10:52 schrieb Kieran Bingham:
>> Hi Umang,
>>
>> + Cc: Matthias
>>
>> Quoting Umang Jain (2024-01-31 05:52:04)
>>> Register 0x3a00 is a reserved field as per the IMX335 datasheet,
>>> hence shouldn't be set by the driver.
>>
>> We still need to explain more about why we're dropping this register
>> write, and what effects it causes.
>>
>> Matthias - I believe this stemmed from the work you did, and I think I
>> recall that you stated this register write broke the CSI2 configuration?
>>
>> Can you clarify anything here for us please?
>
> yes, that's correct.
>
> Since this driver originally did not work in my setup, I came across 
> this register while searching for differences to my working reference 
> configuration.
> With the default value of this register (0x00), the driver works 
> perfectly. With the value previously written to it by the driver 
> (0x01), I cannot receive any frames.
> The problem may depend on the link frequency used.
> I can only use and test a frequency of 445.5MHz on my hardware. Since 
> only link frequencies of 594MHz were supported so far, this may not 
> have been a problem.
>
> Unfortunately I do not have a description of this register, so I can 
> only speculate about the exact cause.

Is it worth to frame the commit message around this speculation ?

My setup has no effect with this register being set or not.
>
> ~Matthias
>
>>
>> -- 
>> Kieran
>>
>>
>>>
>>> Signed-off-by: Umang Jain <umang.jain@...asonboard.com>
>>> ---
>>>   drivers/media/i2c/imx335.c | 1 -
>>>   1 file changed, 1 deletion(-)
>>>
>>> diff --git a/drivers/media/i2c/imx335.c b/drivers/media/i2c/imx335.c
>>> index 7a37eb327ff4..927b4806a5d7 100644
>>> --- a/drivers/media/i2c/imx335.c
>>> +++ b/drivers/media/i2c/imx335.c
>>> @@ -249,7 +249,6 @@ static const struct imx335_reg 
>>> mode_2592x1940_regs[] = {
>>>          {0x3794, 0x7a},
>>>          {0x3796, 0xa1},
>>>          {0x37b0, 0x36},
>>> -       {0x3a00, 0x01},
>>>   };
>>>     static const struct imx335_reg raw10_framefmt_regs[] = {
>>> -- 
>>> 2.41.0
>>>