linux-kernel - Re: [PATCH 6/7] [media] em28xx: add MEDIA

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Message-ID: <5775609.WPlM7VCgVr@wuerfel>
Date:	Tue, 26 Jan 2016 17:51:11 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Mauro Carvalho Chehab <mchehab@....samsung.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Hans Verkuil <hans.verkuil@...co.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] [media] em28xx: add MEDIA_TUNER dependency

On Tuesday 26 January 2016 14:36:44 Mauro Carvalho Chehab wrote:
> Em Tue, 26 Jan 2016 16:53:38 +0100
> Arnd Bergmann <arnd@...db.de> escreveu:
> > On Tuesday 26 January 2016 12:33:08 Mauro Carvalho Chehab wrote:
> > > Em Tue, 26 Jan 2016 15:10:00 +0100
> > > Advanced users may, instead, manually select the media tuner that his
> > > hardware needs. In such case, it doesn't matter if MEDIA_TUNER
> > > is enabled or not.
> > > 
> > > As this is due to a Kconfig limitation, I've no idea how to fix or get
> > > hid of it, but making em28xx dependent of MEDIA_TUNER is wrong.  
> > 
> > I don't understand what limitation you see here. 
> 
> Before MEDIA_TUNER, what we had was something like:
> 
> 	config MEDIA_driver_foo
> 	select VIDEO_tuner_bar if MEDIA_SUBDRV_AUTOSELECT
> 	select MEDIA_frontend_foobar if MEDIA_SUBDRV_AUTOSELECT
> 	...
> 
> However, as different I2C drivers had different dependencies, this
> used to cause lots of troubles. So, one of the Kbuild maintainers
> came out with the idea of converting from select into depends on.
> The MEDIA_TUNER is just an ancillary invisible option to make it
> work at the tuner's side, as usually what we want is to have all
> tuners selected, as we don't have a one to one mapping about what
> driver supports what tuner (nor we wanted to do it, as this would
> mean lots of work for not much gain).

Ok

> > The definition
> > of the VIDEO_TUNER symbol is an empty 'tristate' symbol with a
> > dependency on MEDIA_TUNER to ensure we get a warning if MEDIA_TUNER
> > is not enabled, and to ensure it is set to 'm' if MEDIA_TUNER=m and
> > a "bool" driver selects VIDEO_TUNER.
> 
> No, VIDEO_TUNER is there because we wanted to be able to use select
> to enable V4L2 tuner core support and let people to manually select
> the needed I2C devices with MEDIA_SUBDRV_AUTOSELECT unselected.

I meant what the dependency is there for, not the symbol itself.
It's clear what the symbol does.

> > diff --git a/drivers/media/v4l2-core/Kconfig b/drivers/media/v4l2-core/Kconfig
> > index 9beece00869b..1050bdf1848f 100644
> > --- a/drivers/media/v4l2-core/Kconfig
> > +++ b/drivers/media/v4l2-core/Kconfig
> > @@ -37,7 +37,11 @@ config VIDEO_PCI_SKELETON
> >  # Used by drivers that need tuner.ko
> >  config VIDEO_TUNER
> >  	tristate
> > -	depends on MEDIA_TUNER
> > +
> > +config VIDEO_TUNER_MODULE
> > +	tristate # must not be built-in if MEDIA_TUNER=m because of I2C
> > +	default y if VIDEO_TUNER=y || MEDIA_TUNER=y
> > +	default m if VIDEO_TUNER=m
> 
> Doesn't need to worry about that, because all drivers that select VIDEO_TUNER
> depend on I2C:
> 

Ok, then the dependency does not do anything other than generate a
warning.

> diff --git a/drivers/media/v4l2-core/Kconfig b/drivers/media/v4l2-core/Kconfig
> index 9beece00869b..b30e1c879a57 100644
> --- a/drivers/media/v4l2-core/Kconfig
> +++ b/drivers/media/v4l2-core/Kconfig
> @@ -37,7 +37,7 @@ config VIDEO_PCI_SKELETON
>  # Used by drivers that need tuner.ko
>  config VIDEO_TUNER
>  	tristate
> -	depends on MEDIA_TUNER
> +	default MEDIA_TUNER
>  
>  # Used by drivers that need v4l2-mem2mem.ko
>  config V4L2_MEM2MEM_DEV

So this means it's now enabled if MEDIA_TUNER is enabled, whereas
before it was only enabled when explicitly selected. That sounds
like a useful change, but it also seems unrelated to the warning
fix, and should probably be a separate change, while for now
we can simply remove the 'depends on' line without any replacement.

> Ok, if we'll have platform drivers for analog TV using the I2C bus
> at directly in SoC, then your solution is better, but the tuner core
> driver may not be the best way of doing it. So, for now, I would use
> the simpler version.

Ok. Do you want me to submit a new version or do you prefer to write
one yourself? With or without the 'default'?

	Arnd