genirq: Improve documentation to match current implementation

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Jiri Kosina <trivial@kernel.org>
Link: http://lkml.kernel.org/r/1401178092-1228-3-git-send-email-jiang.liu@linux.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/Documentation/IRQ-domain.txt b/Documentation/IRQ-domain.txt
index 03df71a..8a8b82c 100644
--- a/Documentation/IRQ-domain.txt
+++ b/Documentation/IRQ-domain.txt
@@ -41,8 +41,7 @@
 calling one of the irq_domain_add_*() functions (each mapping method
 has a different allocator function, more on that later).  The function
 will return a pointer to the irq_domain on success.  The caller must
-provide the allocator function with an irq_domain_ops structure with
-the .map callback populated as a minimum.
+provide the allocator function with an irq_domain_ops structure.
 
 In most cases, the irq_domain will begin empty without any mappings
 between hwirq and IRQ numbers.  Mappings are added to the irq_domain