linux-kernel - Re: [PATCH v2 6/6] [media] Only descend into directory when CONFIG_MEDIA

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Date:   Fri, 06 Jan 2017 00:12:13 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     "Andrew F. Davis" <afd@...com>
Cc:     linuxppc-dev@...ts.ozlabs.org,
        Russell King <linux@...linux.org.uk>,
        Miguel Ojeda Sandonis <miguel.ojeda.sandonis@...il.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Richard Purdie <rpurdie@...ys.net>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Lauro Ramos Venancio <lauro.venancio@...nbossa.org>,
        Aloisio Almeida Jr <aloisio.almeida@...nbossa.org>,
        Samuel Ortiz <sameo@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>, linux-pwm@...r.kernel.org,
        linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org
Subject: Re: [PATCH v2 6/6] [media] Only descend into directory when CONFIG_MEDIA_SUPPORT is set

On Thursday, January 5, 2017 4:35:33 PM CET Andrew F. Davis wrote:
> On 01/05/2017 03:42 PM, Arnd Bergmann wrote:
> > On Thursday, January 5, 2017 3:01:58 PM CET Andrew F. Davis wrote:
> >> @@ -109,7 +109,8 @@ obj-$(CONFIG_SERIO)         += input/serio/
> >>  obj-$(CONFIG_GAMEPORT)         += input/gameport/
> >>  obj-$(CONFIG_INPUT)            += input/
> >>  obj-$(CONFIG_RTC_LIB)          += rtc/
> >> -obj-y                          += i2c/ media/
> >> +obj-y                          += i2c/
> >> +obj-$(CONFIG_MEDIA_SUPPORT)    += media/
> >>  obj-$(CONFIG_PPS)              += pps/
> >>  obj-y                          += ptp/
> >>  obj-$(CONFIG_W1)               += w1/
> >>
> > 
> > This one seems wrong: if CONFIG_MEDIA_SUPPORT=m, but some I2C drivers
> > inside of drivers/media/ are built-in, we will fail to enter the directory,
> > see drivers/media/Makefile.
> 
> Not sure if I see this, it looks like everything in drivers/media/
> depends on CONFIG_MEDIA_SUPPORT (directly or indirectly). If
> CONFIG_MEDIA_SUPPORT is =m then all dependents should be locked out of
> being built-in.
> 
> Any bool symbol that controls compilation of source that depends on a
> tristate symbol is broken and should be fixed anyway.

I don't think it's this easy, we have a couple of cases where that doesn't
work. I have not looked at the media example in detail, but at least it
looks intentional.

Note that drivers/media is rather creative with expressing dependencies.

	Arnd