ARM: 6940/1: fiq: Briefly document driver responsibilities for suspend/resume

Drivers which make use of the FIQ interrupt may require the state
of the FIQ mode registers to be preserved across suspend/resume.

Because the FIQ mode registers are not saved and restored
automatically by the kernel, driver authors will need to do the
appropriate save/restore in their own driver suspend/resume
handlers.

Implementing global automatic save/restore of the FIQ state does
not appear appropriate, since this by itself is not sufficient for
FIQ-based drivers to function correctly across suspend/resume in
any case.

This patch adds a brief explanatory note to fiq.h documenting the
requirement placed on driver authors.

Signed-off-by: Dave Martin <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

arch/arm/include/asm/fiq.h

···
  * Support for FIQ on ARM architectures.
  * Written by Philip Blundell <[e-mail]>, 1998
  * Re-written by Russell King
+ *
+ * NOTE: The FIQ mode registers are not magically preserved across
+ * suspend/resume.
+ *
+ * Drivers which require these registers to be preserved across power
+ * management operations must implement appropriate suspend/resume handlers to
+ * save and restore them.
  */
 
 #ifndef __ASM_FIQ_H