Bug 195573

Summary: when using kernel version >=4.9, we can not create md device with minor num exceed 512
Product: Drivers Reporter: Jamie (zjm00111100)
Component: OtherAssignee: drivers_other
Status: NEW ---    
Severity: normal CC: zjm00111100
Priority: P1    
Hardware: All   
OS: Linux   
Kernel Version: 4.9 Subsystem:
Regression: No Bisected commit-id:

Description Jamie 2017-04-25 11:45:07 UTC 
eg:
1. mknod /dev/test b 9 512(any num more then 512) 
2. open /dev/test return ENXIO

what we expect:
1. mknod /dev/test b 9 512(or other numbers)
2.open /dev/test successfully

When I compared the source codes of kernel 4.9 and kernel 3.10, I found this :

static int __init md_init(void)
{
	...

	blk_register_region(MKDEV(MD_MAJOR, 0), 512, THIS_MODULE,
			    md_probe, NULL, NULL);// I don't know the reason of this change . 1UL<<MINORBITS, ===> 512
	blk_register_region(MKDEV(mdp_major, 0), 1UL<<MINORBITS, THIS_MODULE,
			    md_probe, NULL, NULL);

       ...

	md_geninit();
	return 0;

Why did we change the input parament to 512 ? any one can give me a favor?

Thanks and Regards