linux-kernel - Re: [PATCH v7 1/2] [media] atmel-isc: add the Image Sensor Controller code

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Date:	Tue, 2 Aug 2016 09:32:44 +0200
From:	Hans Verkuil <hverkuil@...all.nl>
To:	"Wu, Songjun" <Songjun.Wu@...rochip.com>, nicolas.ferre@...el.com
Cc:	robh@...nel.org, laurent.pinchart@...asonboard.com,
	linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>,
	Niklas SÃ¶derlund 
	<niklas.soderlund+renesas@...natech.se>,
	Benoit Parrot <bparrot@...com>, linux-kernel@...r.kernel.org,
	Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
	Sudip Mukherjee <sudipm.mukherjee@...il.com>,
	Kamil Debski <kamil@...as.org>,
	Tiffany Lin <tiffany.lin@...iatek.com>,
	Peter Griffin <peter.griffin@...aro.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Mikhail Ulyanov <mikhail.ulyanov@...entembedded.com>,
	Richard Röjfors <richard@...finpack.se>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	Simon Horman <horms+renesas@...ge.net.au>
Subject: Re: [PATCH v7 1/2] [media] atmel-isc: add the Image Sensor Controller
 code



On 08/02/2016 08:20 AM, Wu, Songjun wrote:
>>> +static unsigned int sensor_preferred = 1;
>>> +module_param(sensor_preferred, uint, S_IRUGO|S_IWUSR);
>>> +MODULE_PARM_DESC(sensor_preferred,
>>> +		 "Sensor is preferred to output the specified format (1-on 0-off) default 1");
>>
>> I have no idea what this means. Can you elaborate? Why would you want to set this to 0?
>>
> ISC can convert the raw format to the other format, e.g. YUYV.
> If we want to output YUYV format, there are two choices, one is the 
> sensor output YUYV format, ISC bypass the data to the memory, the other 
> is the sensor output raw format, ISC convert raw format to YUYV.
> 
> So I provide a module parameter to user to select.
> I prefer to select the sensor to output the specified format, then I set 
> this parameter to '1', not '0'.

Does this only apply to YUYV?

The reason I am hesitant about this option is that I am not convinced you need
it. The default (sensor preferred) makes sense and that's what other drivers
do as well. Unless you know of a real use-case where you want to set this to 0,
I would just drop this option.

If there *is* a real use-case, then split off adding this module option into a
separate patch so we can discuss it more without blocking getting this driver
into mainline. I don't like the way this is done here.

Regards,

	Hans