sparse annotation question

[Keith Owens <kaos@ocs.com.au>]

This fragment of ia64 code calculates the address of a user space
location, starting from a kernel derived (i.e. not user supplied)
pointer.  put_user() has to be used because the code is running in
interrupt context and the calculated target address may be invalid or
paged out.

func (long regno, unsigned long *contents)
{
	unsigned long i, *bsp;
	mm_segment_t old_fs;
	bsp = <expression involving only kernel variables>;
	old_fs = set_fs(KERNEL_DS);
	for (i = 0; i < (regno - 32); ++i)
		bsp = ia64_rse_skip_regs(bsp, 1);
	put_user(*contents, bsp);
	set_fs(old_fs);
}

sparse is complaining that the second parameter to put_user() is not
marked as __user.  How do I tell sparse to ignore this case?  Marking
bsp as __user does not work, sparse then complains about incorrect type
in assignment (different address spaces).