linux-kernel - Re: [PATCH mmotm] hid-picolcd: depends on LCD_CLASS

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Message-ID: <20100406183535.7de3c628@neptune.home>
Date:	Tue, 6 Apr 2010 18:35:35 +0200
From:	Bruno Prémont <bonbons@...ux-vserver.org>
To:	Randy Dunlap <randy.dunlap@...cle.com>
Cc:	Jiri Kosina <jkosina@...e.cz>, linux-kernel@...r.kernel.org,
	linux-input@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, rvinyard@...nmsu.edu
Subject: Re: [PATCH mmotm] hid-picolcd: depends on LCD_CLASS_DEVICE

On Tue, 06 April 2010 Randy Dunlap <randy.dunlap@...cle.com> wrote:
> On Tue, 6 Apr 2010 10:56:35 +0200 Bruno Prémont wrote:
> 
> > On Tue, 6 Apr 2010 10:40:06 +0200 Jiri Kosina <jkosina@...e.cz> wrote:
> > > 
> > > [ adding Bruno to CC ]
> > > 
> > > On Mon, 5 Apr 2010, Randy Dunlap wrote:
> > > 
> > > > From: Randy Dunlap <randy.dunlap@...cle.com>
> > > > 
> > > > HID_PICOLCD should depend on LCD_CLASS_DEVICE, otherwise the
> > > > build fails when HID_PICOLCD=y and LCD_CLASS_DEVICE=m:
> > > > 
> > > > hid-picolcd.c:(.text+0x84523f): undefined reference to `lcd_device_unregister'
> > > > hid-picolcd.c:(.text+0x8478ab): undefined reference to `lcd_device_register'
> > > > hid-picolcd.c:(.text+0x84c15f): undefined reference to `lcd_device_unregister'
> > 
> > That is weird, the
> > 
> > #if defined(CONFIG_LCD_CLASS_DEVICE) || defined(CONFIG_LCD_CLASS_DEVICE_MODULE)
> >   feature support code
> > #else
> >   empty stubs
> > #endif
> > 
> > blocks should have prevented LCD_CLASS support from being built if it
> > was not enabled in configuration.
> > 
> > Do you have the .config matching your build?
> 
> Yes, it's attached.

Thanks, here is the extract (only the pertinent items):
CONFIG_BACKLIGHT_LCD_SUPPORT=y
CONFIG_LCD_CLASS_DEVICE=m
CONFIG_BACKLIGHT_CLASS_DEVICE=y
CONFIG_HID_PICOLCD=y

It triggers the issue by having PicoLCD built-in while one of the
optional dependencies as a module.

Any idea of how this can be solved with kbuild in order to keep the
dependencies optional?

Something that would satisfy the following pseudocode:
  if CONFIG_HID_PICOLCD == y
    assert(CONFIG_LCD_CLASS_DEVICE != m)


One of my attempts did end up with a circular loop with regard to FB
(some of the FB drivers did select INPUT)?

I had something like:

config HID_PICOLCD
  tristate ...

config HID_PICOLCD_FB
  bool ...
  depends on HID_PICOLCD
  select FB
  select FB_...

...

Then in the code I checked for CONFIG_HID_PICOLCD_FB instead of
(CONFIG_FB or CONFIG_FB_MODULE).

Thanks,
Bruno
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