Initialization ordering problem

[William Jhun]

On Tue, Mar 19, 2002 at 07:50:12AM +0100, Jonas Holmberg wrote:
> On Tue, 2002-03-19 at 07:14, William Jhun wrote:
> > I could work up some kludge to make
> > our platform-specific flash initialization code link in after the mtd
> > code, but this would be ugly.
> 
> Why don't you want to change the link order? Isn't it logical to link in
> the architecture independent parts before the architecture speficic ones
> so that the arch specific code can use the frameworks in the arch
> independent code?

Hm, this isn't immediately logical to me. I would think that the
platform-dependent setup would have to take place to set up any
subsystems that may be used by the different drivers. I'm not clear on
this one.

This would require linking "$(CORE_FILES)" last in the vmlinux link
order (top-level Makefile):

***************
*** 261,268 ****
  vmlinux: include/linux/version.h $(CONFIGURATION) init/main.o init/version.o linuxsubdirs
  	$(LD) $(LINKFLAGS) $(HEAD) init/main.o init/version.o \
  		--start-group \
- 		$(CORE_FILES) \
  		$(DRIVERS) \
  		$(NETWORKS) \
  		$(LIBS) \
  		--end-group \
--- 261,268 ----
  vmlinux: include/linux/version.h $(CONFIGURATION) init/main.o init/version.o linuxsubdirs
  	$(LD) $(LINKFLAGS) $(HEAD) init/main.o init/version.o \
  		--start-group \
  		$(DRIVERS) \
+ 		$(CORE_FILES) \
  		$(NETWORKS) \
  		$(LIBS) \
  		--end-group \

I may try this temporarily, but is this the "correct" way to deal with
the problem? I'm not sure it would even work.

What I don't understand is why the MTD code depends on separate
__initcall functions to execute for complete initialization - isn't it
possible to create, if the MTD code is being linked directly in the
kernel, a static array of subsystems that need to be initialized or a
list of callbacks? A brief glance shows that the Linux IDE code attempts
to do something similar (drivers/ide/ide.c, ide_init_builtin_drivers()):

        /*
         * Attempt to match drivers for the available drives
         */
#ifdef CONFIG_BLK_DEV_IDEDISK
        (void) idedisk_init();
#endif /* CONFIG_BLK_DEV_IDEDISK */
#ifdef CONFIG_BLK_DEV_IDECD
        (void) ide_cdrom_init();
#endif /* CONFIG_BLK_DEV_IDECD */
#ifdef CONFIG_BLK_DEV_IDETAPE
        (void) idetape_init();
#endif /* CONFIG_BLK_DEV_IDETAPE */
#ifdef CONFIG_BLK_DEV_IDEFLOPPY
        (void) idefloppy_init();
#endif /* CONFIG_BLK_DEV_IDEFLOPPY */
#ifdef CONFIG_BLK_DEV_IDESCSI
 #ifdef CONFIG_SCSI
        (void) idescsi_init();
 #else
    #warning ide scsi-emulation selected but no SCSI-subsystem in kernel
 #endif
#endif /* CONFIG_BLK_DEV_IDESCSI */

Would something like this be warranted? It sounds like 2.5.x offers some
neat features, but we're not there yet - we're stuck with 2.4.x kernels
at the moment.

Thanks,
Will