linux-kernel - Re: [PATCH v2 0/7] [PATCH v2 0/7] Add support of OV9655 camera

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Message-Id: <BCD1BD18-96E3-4638-8935-B5C832D8EE52@goldelico.com>
Date:   Tue, 18 Jul 2017 14:17:36 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Hugues Fruchet <hugues.fruchet@...com>,
        Sylwester Nawrocki <snawrocki@...nel.org>,
        Hans Verkuil <hverkuil@...all.nl>
Cc:     Guennadi Liakhovetski <g.liakhovetski@....de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        devicetree <devicetree@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Yannick Fertre <yannick.fertre@...com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-media@...r.kernel.org
Subject: Re: [PATCH v2 0/7] [PATCH v2 0/7] Add support of OV9655 camera

Hi,

> Am 18.07.2017 um 13:59 schrieb Hans Verkuil <hverkuil@...all.nl>:
> 
> On 12/07/17 22:01, Sylwester Nawrocki wrote:
>> Hi Hugues,
>> 
>> On 07/03/2017 11:16 AM, Hugues Fruchet wrote:
>>> This patchset enables OV9655 camera support.
>>> 
>>> OV9655 support has been tested using STM32F4DIS-CAM extension board
>>> plugged on connector P1 of STM32F746G-DISCO board.
>>> Due to lack of OV9650/52 hardware support, the modified related code
>>> could not have been checked for non-regression.
>>> 
>>> First patches upgrade current support of OV9650/52 to prepare then
>>> introduction of OV9655 variant patch.
>>> Because of OV9655 register set slightly different from OV9650/9652,
>>> not all of the driver features are supported (controls). Supported
>>> resolutions are limited to VGA, QVGA, QQVGA.
>>> Supported format is limited to RGB565.
>>> Controls are limited to color bar test pattern for test purpose.
>> 
>> I appreciate your efforts towards making a common driver but IMO it would be 
>> better to create a separate driver for the OV9655 sensor.  The original driver 
>> is 1576 lines of code, your patch set adds half of that (816).  There are
>> significant differences in the feature set of both sensors, there are 
>> differences in the register layout.  I would go for a separate driver, we  
>> would then have code easier to follow and wouldn't need to worry about possible
>> regressions.  I'm afraid I have lost the camera module and won't be able 
>> to test the patch set against regressions.
>> 
>> IMHO from maintenance POV it's better to make a separate driver. In the end 
>> of the day we wouldn't be adding much more code than it is being done now.
> 
> I agree. We do not have great experiences in the past with trying to support
> multiple variants in a single driver (unless the diffs are truly small).

Well,
IMHO the diffs in ov965x are smaller (but untestable because nobody seems
to have an ov9650/52 board) than within the bq27xxx chips, but I can dig out
an old pdata based separate ov9655 driver and extend that to become DT compatible.

I had abandoned that separate approach in favour of extending the ov965x driver.

Have to discuss with Hugues how to proceed.

BR and thanks,
Nikolaus