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

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:

quoted

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 <redacted>
---
  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