Re: [RFC] Move some soc-camera drivers to staging in preparation for removal

[Hans Verkuil <hverkuil@xs4all.nl>]

On 02/19/2016 05:24 PM, Mauro Carvalho Chehab wrote:
> Em Fri, 19 Feb 2016 14:24:08 +0100
> Hans Verkuil <hverkuil@xs4all.nl> escreveu:
> 
>> Hi all,
>>
>> The soc-camera framework is a problem for reusability of sub-device drivers since
>> those need access to the soc-camera framework. Which defeats the purpose of the
>> sub-device framework. It is the reason why we still have a media/i2c/soc-camera
>> directory for subdevs that can only work with soc-camera.
>>
>> Ideally I would like to drop soc-camera completely, but it is still in use.
>>
>> One of the largest users is Renesas with their r-car SoC, but Niklas Söderlund
>> made a replacement driver that should make it possible to remove the soc-camera
>> r-car driver, hopefully this year.
>>
>> What I would like to do is to move soc-camera drivers that we consider obsolete
>> to staging, and remove them in 1-2 kernel cycles if nobody steps up.
>>
>> See also this past thread from Guennadi:
>>
>> http://www.spinics.net/lists/linux-media/msg89253.html
>>
>> And yes, I said in that thread that I was OK with keeping soc-camera as-is. But
>> it still happens that companies pick this framework for new devices (the driver
>> for the Tegra K1 for example). It is another reason besides the reusability issue
>> for remove this framework more aggressively then I intended originally.
>>
>>
>> We have the following drivers:
>>
>> - pxa_camera for the PXA27x Quick Capture Interface
>>
>>   Apparently this architecture still gets attention (see the link to the thread
>>   above). But it does use vb1 which we really want to phase out soon. Does anyone
>>   know if this driver still works with the latest kernel? Because it is using vb1
>>   it is a strong candidate for removing it (or replacing it with something better
>>   if someone steps up).
>>
>> - mx2_camera: i.MX27 Camera Sensor Interface
>>
>>   Have not seen any development since April 2013 (mx2-camera: move interface
>>   activation and deactivation to clock callbacks by Guennadi). No idea if it still
>>   works or if it is still in use. Does anyone know?
>>
>> - mx3_camera: i.MX3x Camera Sensor Interface
>>
>>   Have not seen any development since July 2013 (add support for asynchronous
>>   subdevice registration by Guennadi). Same as for mx2_camera: does it still work?
>>   Is it still in use?
>>
>> - omap1_camera: OMAP1 Camera Interface
>>
>>   It uses vb1, so that's one very good reason for removing it. And as far as I
>>   know it is unused and likely won't work.
>>
>> - sh_mobile_ceu_camera: SuperH Mobile CEU Interface
>>
>>   I worked on this, but I know it does function anymore. I'd say that this can
>>   be removed.
>>
>> - sh_mobile_csi2: SuperH Mobile MIPI CSI-2 Interface
>>
>>   I don't have hardware to test, but I'd be surprised if it still works. Can
>>   someone test? If it is broken, then it can be moved to staging.
>>
>> - rcar_vin: R-Car Video Input (VIN)
>>   Will be replaced with a regular driver as mentioned above.
>>
>> - atmel-isi: ATMEL Image Sensor Interface (ISI)
>>
>>   I believe this is still actively maintained. Would someone be willing to
>>   convert this? It doesn't look like a complex driver.
>>
>> Now I am not planning to remove soc-camera (yet), but at least we should get
>> rid of unmaintained drivers, especially if they don't work anymore or if they
>> use the old vb1 mess.
>>
>> And we can then take a good look at what remains.
> 
> You're forgetting the I2C sensor cam drivers. There are 14 such drivers
> under drivers/media/i2c/soc_camera/.

I didn't forget those, but I thought that we should tackle those later.
It's not so easy to remove the soc-camera dependency from them. I tried
that once, and I think I could only make one or two of those drivers soc-camera
independent :-(

And without hardware you have no idea if they still work.

The code is still available in git, even if we remove them. I don't really
like the idea of keeping code in the kernel that very likely won't work after
the soc-camera dependencies are removed.

Regards,

	Hans

> 
> I guess we should try to remove the soc_camera.h dependency from them,
> making the still alive drivers to use the I2C sensor drivers directly.
> 
> The point is that such sensors could be useful somewhere else.
> For example, there are at least one or two such drivers that could be used
> on em28xx-based cameras to replace some really ugly hacks there. Also,
> gspca have sensor i2c code hardcoded on it.
> 
> So, I would hate to lose those sensor drivers in the process.
> 
> Regards,
> Mauro
>