OMAP2+: hwmod: upgrade per-hwmod mutex to a spinlock

Change the per-hwmod mutex to a spinlock.  (The per-hwmod lock
serializes most post-initialization hwmod operations such as enable,
idle, and shutdown.)  Spinlocks are needed, because in some cases,
hwmods must be enabled from timer interrupt disabled-context, such as
an ISR.  The current use-case that is driving this is the OMAP GPIO
block ISR: it can trigger interrupts even with its clocks disabled,
but these clocks are needed for register accesses in the ISR to succeed.

This patch also effectively reverts commit
848240223c35fcc71c424ad51a8e8aef42d3879c - this patch makes
_omap_hwmod_enable() and _omap_hwmod_init() static, renames them back
to _enable() and _idle(), and changes their callers to call the
spinlocking versions.  Previously, since omap_hwmod_{enable,init}()
attempted to take mutexes, these functions could not be called while
the timer interrupt was disabled; but now that the functions use
spinlocks and save and restore the IRQ state, it is appropriate to
call them directly.

Kevin Hilman <khilman@deeprootsystems.com> originally proposed this
patch - thanks Kevin.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Benoît Cousson <b-cousson@ti.com>

1 files changed, 2 insertions, 7 deletions

diff --git a/arch/arm/mach-omap2/serial.c b/arch/arm/mach-omap2/serial.c
index 9dc077e2d8af..0548bbd43407 100644
--- a/arch/arm/mach-omap2/serial.c
+++ b/arch/arm/mach-omap2/serial.c
@@ -106,21 +106,16 @@ struct omap_uart_state {
 static LIST_HEAD(uart_list);
 static u8 num_uarts;
 
-/*
- * Since these idle/enable hooks are used in the idle path itself
- * which has interrupts disabled, use the non-locking versions of
- * the hwmod enable/disable functions.
- */
 static int uart_idle_hwmod(struct omap_device *od)
 {
-	_omap_hwmod_idle(od->hwmods[0]);
+	omap_hwmod_idle(od->hwmods[0]);
 
 	return 0;
 }
 
 static int uart_enable_hwmod(struct omap_device *od)
 {
-	_omap_hwmod_enable(od->hwmods[0]);
+	omap_hwmod_enable(od->hwmods[0]);
 
 	return 0;
 }