linux-kernel - Re: [PATCH] media: Kconfig: Make DVB_CORE=m possible when MEDIA

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Date:   Wed, 6 Oct 2021 11:26:35 +0800
From:   Lecopzer Chen <lecopzer.chen@...iatek.com>
To:     <mchehab@...nel.org>
CC:     <lecopzer.chen@...iatek.com>, <linux-kernel@...r.kernel.org>,
        <linux-media@...r.kernel.org>, <yj.chiang@...iatek.com>
Subject: Re: [PATCH] media: Kconfig: Make DVB_CORE=m possible when MEDIA_SUPPORT=y

> > A case that we need VIDEO_DEV=y but DVB_CORE=m, and this doesn't
> > work since DVB_CORE is default MEDIA_DIGITAL_TV_SUPPORT and then
> > follows MEDIA_SUPPORT.
> > 
> > Change to tristate to make DVB_CORE=m possible when MEDIA_SUPPORT=y
> > 
> > Signed-off-by: Lecopzer Chen <lecopzer.chen@...iatek.com>
> > ---
> >  drivers/media/Kconfig | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/media/Kconfig b/drivers/media/Kconfig
> > index b07812657cee..c3baf92b4d02 100644
> > --- a/drivers/media/Kconfig
> > +++ b/drivers/media/Kconfig
> > @@ -88,7 +88,7 @@ config MEDIA_ANALOG_TV_SUPPORT
> >  		will disable support for them.
> >  
> >  config MEDIA_DIGITAL_TV_SUPPORT
> > -	bool
> > +	tristate
> >  	prompt "Digital TV" if MEDIA_SUPPORT_FILTER
> >  	default y if !MEDIA_SUPPORT_FILTER
> >  	help
> 
> While this change looks simple enough, not sure if this would work
> for all possibilities. If I'm not mistaken, someone proposed
> something similar to it, but it caused troubles with different
> configurations. I don't recall any patch addressing it, but I
> may be wrong.
> 
> Tf I remember correctly, the problem rises when either V4L or DVB
> core is compiled as module and the other one is compiled builtin.
> On such scenario, all drivers that depend on both should be
> compiled as a module, or the build will fail.

I've had a quick test:

CONFIG_MEDIA_SUPPORT=y
CONFIG_MEDIA_SUPPORT_FILTER=y
CONFIG_MEDIA_SUBDRV_AUTOSELECT=y
CONFIG_MEDIA_DIGITAL_TV_SUPPORT=m
CONFIG_DVB_CORE=m
In this set, all the module depends on DVB_CORE
will be =m even if I manually change .config.

I'm not sure which config or module would build failed if DVB is module,
but IMO, any module has explicitly depends on DVB_CORE would follow the
configuation of DVB_CORE, and
the only possible case which build failed should be those
modules need to depend on DVB_CORE but didn't explicitly write
in Kconfig.
Also, I have no idea why someone needs DVB_CORE=m but other modules
depend on it need =y.

If anything I can test please tell me, thanks.


Thanks,
Lecopzer