Re: [PATCH 5/7] omapfb: omapfb_dss.h: add stubs to build with COMPILE_TEST && DRM_OMAP

[Mauro Carvalho Chehab <mchehab@s-opensource.com>]

Em Mon, 23 Apr 2018 22:48:06 +0300
Laurent Pinchart <laurent.pinchart@ideasonboard.com> escreveu:

> Hi Mauro,
> 
> On Monday, 23 April 2018 17:22:27 EEST Mauro Carvalho Chehab wrote:
> > Em Mon, 23 Apr 2018 15:56:53 +0200 Bartlomiej Zolnierkiewicz escreveu:  
> > > On Monday, April 23, 2018 02:47:28 PM Bartlomiej Zolnierkiewicz wrote:  
> > >> On Friday, April 20, 2018 01:42:51 PM Mauro Carvalho Chehab wrote:  
> > >>> Add stubs for omapfb_dss.h, in the case it is included by
> > >>> some driver when CONFIG_FB_OMAP2 is not defined, with can
> > >>> happen on ARM when DRM_OMAP is not 'n'.
> > >>> 
> > >>> That allows building such driver(s) with COMPILE_TEST.
> > >>> 
> > >>> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>  
> > >> 
> > >> This patch should be dropped (together with patch #6/7) as it was
> > >> superseded by a better solution suggested by Laurent:
> > >> 
> > >> https://patchwork.kernel.org/patch/10325193/
> > >> 
> > >> ACK-ed by Tomi:
> > >> 
> > >> https://www.spinics.net/lists/dri-devel/msg171918.html
> > >> 
> > >> and already merged by you (commit 7378f1149884 "media: omap2:
> > >> omapfb: allow building it with COMPILE_TEST")..  
> > > 
> > > Hmm, I see now while this patch is still included:
> > > 
> > > menuconfig FB_OMAP2
> > >         tristate "OMAP2+ frame buffer support"
> > >         depends on FB
> > >         depends on DRM_OMAP = n
> > > 
> > > Ideally we should be able to build both drivers in the same kernel
> > > (especially as modules).
> > > 
> > > I was hoping that it could be fixed easily but then I discovered
> > > the root source of the problem:
> > > 
> > > drivers/gpu/drm/omapdrm/dss/display.o: In function
> > > `omapdss_unregister_display': display.c:(.text+0x2c): multiple definition
> > > of `omapdss_unregister_display'
> > > drivers/video/fbdev/omap2/omapfb/dss/display.o:display.c:(.text+0x198):
> > > first defined here ...  
> > 
> > Yes, and declared on two different places:
> > 
> > drivers/gpu/drm/omapdrm/dss/omapdss.h:void omapdss_unregister_display(struct
> > omap_dss_device *dssdev); include/video/omapfb_dss.h:void
> > omapdss_unregister_display(struct omap_dss_device *dssdev);
> > 
> > one alternative would be to give different names to it, and a common
> > header for both.
> > 
> > At such header, it could be doing something like:
> > 
> > static inline void omapdss_unregister_display(struct omap_dss_device
> > *dssdev) {
> > #if enabled(CONFIG_DRM_OMAP)
> > 	omapdss_unregister_display_drm(struct omap_dss_device *dssdev);
> > #else
> > 	omapdss_unregister_display_fb(struct omap_dss_device *dssdev);
> > ##endif
> > }
> > 
> > Yet, after a very quick check, it seems that nowadays only the
> > media omap driver uses the symbols at FB_OMAP:
> > 
> > $ git grep omapfb_dss.h
> > drivers/media/platform/omap/omap_vout.c:#include <video/omapfb_dss.h>
> > drivers/media/platform/omap/omap_voutdef.h:#include <video/omapfb_dss.h>
> > drivers/media/platform/omap/omap_voutlib.c:#include <video/omapfb_dss.h>
> > 
> > So, perhaps just renaming the common symbols and changing FB_OMAP2 to:
> > 
> > 	menuconfig FB_OMAP2
> > 	         tristate "OMAP2+ frame buffer support"
> > 	         depends on FB
> > 	         depends on (DRM_OMAP = n) || COMPILE_TEST
> > 
> > would be enough to allow to build both on ARM.  
> 
> I don't think it's worth it renaming the common symbols. They will change over 
> time as omapdrm is under heavy rework, and it's painful enough without having 
> to handle cross-tree changes.

It could just rename the namespace-conflicting FB_OMAP2 functions,
keeping the DRM ones as-is.

> Let's just live with the fact that both drivers 
> can't be compiled at the same time, given that omapfb is deprecated.

IMO, a driver that it is deprecated, being in a state where it
conflicts with a non-deprecated driver that is under heavy rework
is a very good candidate to go to drivers/staging or even to /dev/null.

Thanks,
Mauro