Re: [PATCH] staging: sm750: Fix missing config in Kconfig

[Vinicius Peixoto]

Hi Greg,

On 10/9/24 06:56, Greg Kroah-Hartman wrote:
> On Sat, Sep 21, 2024 at 03:06:09PM -0300, Fabricio Gasperin wrote:
> > Fixes the following compilation error:
> >
> > ERROR: modpost: "fb_io_read" [drivers/staging/sm750fb/sm750fb.ko] undefined!
> > ERROR: modpost: "fb_io_write" [drivers/staging/sm750fb/sm750fb.ko] undefined!
> > ERROR: modpost: "fb_io_mmap" [drivers/staging/sm750fb/sm750fb.ko] undefined!
> >
> > Signed-off-by: Fabricio Gasperin <fgasperin@xxxxxxxxxx>
> > ---
> >   drivers/staging/sm750fb/Kconfig | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/staging/sm750fb/Kconfig b/drivers/staging/sm750fb/Kconfig
> > index 08bcccdd0f1c..eca1aa43d725 100644
> > --- a/drivers/staging/sm750fb/Kconfig
> > +++ b/drivers/staging/sm750fb/Kconfig
> > @@ -3,6 +3,7 @@ config FB_SM750
> >   	tristate "Silicon Motion SM750 framebuffer support"
> >   	depends on FB && PCI && HAS_IOPORT
> >   	select FB_MODE_HELPERS
> > +	select FB_IOMEM_FOPS
> >   	select FB_CFB_FILLRECT
> >   	select FB_CFB_COPYAREA
> >   	select FB_CFB_IMAGEBLIT
> > --
> > 2.46.1
>
> What is causing this error? What commit created the problem, and why
> has no one reported it yet?

This happens because drivers/staging/sm750fb/sm750.c, defines an fb_ops 
structure:

static const struct fb_ops lynxfb_ops = {
	.owner = THIS_MODULE,
	FB_DEFAULT_IOMEM_OPS,
	...
};

FB_DEFAULT_IOMEM_OPS expands to the fb_io_* helpers declared in 
include/linux/fb.h and defined in drivers/video/fbdev/core/fb_io_fops.c; 
however, the latter is gated by FB_IOMEM_FOPS, so when compiling a 
kernel with CONFIG_STAGING=y + CONFIG_FB=m + CONFIG_FB_SM750=m, you get 
the following error:

ERROR: modpost: "fb_io_read" [drivers/staging/sm750fb/sm750fb.ko] undefined!
ERROR: modpost: "fb_io_write" [drivers/staging/sm750fb/sm750fb.ko] 
undefined!
ERROR: modpost: "fb_io_mmap" [drivers/staging/sm750fb/sm750fb.ko] undefined!
make[2]: *** [scripts/Makefile.modpost:145: Module.symvers] Error 1

So in order to solve it we select FB_IOMEM_FOPS, much like the other 
FB_* drivers do in drivers/video/fbdev/Kconfig.

Not entirely sure why this wasn't caught before, but the commit that 
broke the build for sm750fb is 6b180f66c0dd ("fbdev: Provide I/O-memory 
helpers as module"), which made the fb_io_* helpers be built as a 
separate module instead of being bundled in fb.o (which is what sm750fb 
was relying on). I think Fabricio can add a "Fixes:" tag in v2.

Thanks,
Vinicius

> confused,
>
> greg k-h