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

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Date: Wed, 31 Jan 2024 11:32:54 +0100
From: Matthias Fend <matthias.fend@...end.at>
To: Kieran Bingham <kieran.bingham@...asonboard.com>,
 Umang Jain <umang.jain@...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 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.

~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
>>