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

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Message-Id: <20100406095633.49ec957a.randy.dunlap@oracle.com>
Date:	Tue, 6 Apr 2010 09:56:33 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Bruno Prémont <bonbons@...ux-vserver.org>
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, 6 Apr 2010 18:35:35 +0200 Bruno Prémont wrote:

> 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.

Yes, basically what the patch description said.

> 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)
> 

If you don't want the kconfig machinery to do that (it appears that you don't),
then I guess that you'll need to expand the source code to handle
CONFIG_LCD_CLASS_DEVICE=y and CONFIG_LCD_CLASS_DEVICE=m differently.
Or only handle them differently if HID_PICOLCD=y.  :(


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

  (not that I can find)

CONFIG_VT does select INPUT
and CONFIG_DRM_I915 does
	select INPUT if ACPI


> 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).



---
~Randy
(re)read Documentation/ManagementStyle
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