Re: [PATCH] V4L: introduce a Kconfig variable to disable helper-chip autoselection

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Guennadi Liakhovetski wrote:

> Hi Mauro
> 
> we just discussed this with Hans on IRC, and if I understood him 
> correctly, he was of the same opinion, that adding such a variable could 
> help.
> 
> The problem is the following: this automatic selection works in a way, 
> that various bridge drivers select "helper" chip drivers (i2c subdevice 
> drivers" if this autoselection is enabled, e.g.
> 
> config VIDEO_MXB
> 	tristate "Siemens-Nixdorf 'Multimedia eXtension Board'"
> 	depends on PCI && VIDEO_V4L1 && I2C
> 	select VIDEO_SAA7146_VV
> 	select VIDEO_TUNER
> 	select VIDEO_SAA711X if VIDEO_HELPER_CHIPS_AUTO
> 	select VIDEO_TDA9840 if VIDEO_HELPER_CHIPS_AUTO
> 	select VIDEO_TEA6415C if VIDEO_HELPER_CHIPS_AUTO
> 	select VIDEO_TEA6420 if VIDEO_HELPER_CHIPS_AUTO
> 
> With SoC-based set ups this cannot work. The only location where this 
> information is available is platform code under arch/... and selecting 
> these drivers from there would be awkward imho.

Kconfig works fine if the var is on another place. So, you could do things
like:

config VIDEO_xxx
	select VIDEO_foo if VIDEO_HELPER_CHIPS_AUTO && ARCH_bar

You may even convert it into dependencies like:

config VIDEO_I2C_foo
	depends on ARCH_bar && config VIDEO_xxx
	default y if VIDEO_HELPER_CHIPS_AUTO

The depends on syntax generally works better than using select. We've converted
some select into depends on a few places like tuner, like, for example:

config MEDIA_TUNER_TDA827X
        tristate "Philips TDA827X silicon tuner"
        depends on VIDEO_MEDIA && I2C
        default m if MEDIA_TUNER_CUSTOMISE

> So, for example, we want 
> to put the ak881x video encoder driver under
> 
> comment "Video encoders"
> 
> and those drivers are only visible if VIDEO_HELPER_CHIPS_AUTO is 
> unselected, and if it is selected, which it is by default, there is noone 
> to automatically select ak881x. So, I think, the proposed patch is not a 
> work-around, but a reasonable solution for this issue.

Even the menu being invisible, any of the above logic would work, if you do
something like:

config VIDEO_AK881X
	depends on ARCH_MX1 && I2C
	default y if VIDEO_HELPER_CHIPS_AUTO && SOC_CAMERA

or:

config SOC_CAMERA
	select VIDEO_AK881X if VIDEO_HELPER_CHIPS_AUTO && ARCH_MX1

You should just take some care, since there are some combinations that won't work.
For example, if SOC_CAMERA is a module, any ancillary drivers used by it should also
be 'm', otherwise, the driver will break. That's why, when having multiple
dependencies, the better is to use the "depends on" way.


> 
> Thanks
> Guennadi
> ---
> Guennadi Liakhovetski, Ph.D.
> Freelance Open-Source Software Developer
> http://www.open-technology.de/
> --
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-- 

Cheers,
Mauro