IRQ: Maintain regs pointer globally rather than passing to IRQ handlers

Maintain a per-CPU global "struct pt_regs *" variable which can be used instead
of passing regs around manually through all ~1800 interrupt handlers in the
Linux kernel.

The regs pointer is used in few places, but it potentially costs both stack
space and code to pass it around.  On the FRV arch, removing the regs parameter
from all the genirq function results in a 20% speed up of the IRQ exit path
(ie: from leaving timer_interrupt() to leaving do_IRQ()).

Where appropriate, an arch may override the generic storage facility and do
something different with the variable.  On FRV, for instance, the address is
maintained in GR28 at all times inside the kernel as part of general exception
handling.

Having looked over the code, it appears that the parameter may be handed down
through up to twenty or so layers of functions.  Consider a USB character
device attached to a USB hub, attached to a USB controller that posts its
interrupts through a cascaded auxiliary interrupt controller.  A character
device driver may want to pass regs to the sysrq handler through the input
layer which adds another few layers of parameter passing.

I've build this code with allyesconfig for x86_64 and i386.  I've runtested the
main part of the code on FRV and i386, though I can't test most of the drivers.
I've also done partial conversion for powerpc and MIPS - these at least compile
with minimal configurations.

This will affect all archs.  Mostly the changes should be relatively easy.
Take do_IRQ(), store the regs pointer at the beginning, saving the old one:

	struct pt_regs *old_regs = set_irq_regs(regs);

And put the old one back at the end:

	set_irq_regs(old_regs);

Don't pass regs through to generic_handle_irq() or __do_IRQ().

In timer_interrupt(), this sort of change will be necessary:

	-	update_process_times(user_mode(regs));
	-	profile_tick(CPU_PROFILING, regs);
	+	update_process_times(user_mode(get_irq_regs()));
	+	profile_tick(CPU_PROFILING);

I'd like to move update_process_times()'s use of get_irq_regs() into itself,
except that i386, alone of the archs, uses something other than user_mode().

Some notes on the interrupt handling in the drivers:

 (*) input_dev() is now gone entirely.  The regs pointer is no longer stored in
     the input_dev struct.

 (*) finish_unlinks() in drivers/usb/host/ohci-q.c needs checking.  It does
     something different depending on whether it's been supplied with a regs
     pointer or not.

 (*) Various IRQ handler function pointers have been moved to type
     irq_handler_t.

Signed-Off-By: David Howells <dhowells@redhat.com>
(cherry picked from 1b16e7ac850969f38b375e511e3fa2f474a33867 commit)

6 files changed, 9 insertions, 10 deletions

diff --git a/drivers/parisc/dino.c b/drivers/parisc/dino.c
index 0d96c50..a0a8fd8 100644
--- a/drivers/parisc/dino.c
+++ b/drivers/parisc/dino.c
@@ -368,8 +368,7 @@ static struct hw_interrupt_type dino_interrupt_type = {
  * ilr_loop counter is a kluge to prevent a "stuck" IRQ line from
  * wedging the CPU. Could be removed or made optional at some point.
  */
-static irqreturn_t
-dino_isr(int irq, void *intr_dev, struct pt_regs *regs)
+static irqreturn_t dino_isr(int irq, void *intr_dev)
 {
 	struct dino_device *dino_dev = intr_dev;
 	u32 mask;
diff --git a/drivers/parisc/eisa.c b/drivers/parisc/eisa.c
index 884965c..094562e 100644
--- a/drivers/parisc/eisa.c
+++ b/drivers/parisc/eisa.c
@@ -199,7 +199,7 @@ static struct hw_interrupt_type eisa_interrupt_type = {
 	.end =		no_end_irq,
 };
 
-static irqreturn_t eisa_irq(int wax_irq, void *intr_dev, struct pt_regs *regs)
+static irqreturn_t eisa_irq(int wax_irq, void *intr_dev)
 {
 	int irq = gsc_readb(0xfc01f000); /* EISA supports 16 irqs */
 	unsigned long flags;
@@ -249,7 +249,7 @@ static irqreturn_t eisa_irq(int wax_irq, void *intr_dev, struct pt_regs *regs)
 	return IRQ_HANDLED;
 }
 
-static irqreturn_t dummy_irq2_handler(int _, void *dev, struct pt_regs *regs)
+static irqreturn_t dummy_irq2_handler(int _, void *dev)
 {
 	printk(KERN_ALERT "eisa: uhh, irq2?\n");
 	return IRQ_HANDLED;
diff --git a/drivers/parisc/gsc.c b/drivers/parisc/gsc.c
index b45aa5c..1b3e3fd 100644
--- a/drivers/parisc/gsc.c
+++ b/drivers/parisc/gsc.c
@@ -73,7 +73,7 @@ EXPORT_SYMBOL(gsc_alloc_irq);
 EXPORT_SYMBOL(gsc_claim_irq);
 
 /* Common interrupt demultiplexer used by Asp, Lasi & Wax.  */
-irqreturn_t gsc_asic_intr(int gsc_asic_irq, void *dev, struct pt_regs *regs)
+irqreturn_t gsc_asic_intr(int gsc_asic_irq, void *dev)
 {
 	unsigned long irr;
 	struct gsc_asic *gsc_asic = dev;
@@ -87,7 +87,7 @@ irqreturn_t gsc_asic_intr(int gsc_asic_irq, void *dev, struct pt_regs *regs)
 	do {
 		int local_irq = __ffs(irr);
 		unsigned int irq = gsc_asic->global_irq[local_irq];
-		__do_IRQ(irq, regs);
+		__do_IRQ(irq);
 		irr &= ~(1 << local_irq);
 	} while (irr);
 
diff --git a/drivers/parisc/gsc.h b/drivers/parisc/gsc.h
index a3dc456..762a1ba 100644
--- a/drivers/parisc/gsc.h
+++ b/drivers/parisc/gsc.h
@@ -44,4 +44,4 @@ void gsc_fixup_irqs(struct parisc_device *parent, void *ctrl,
 		void (*choose)(struct parisc_device *child, void *ctrl));
 void gsc_asic_assign_irq(struct gsc_asic *asic, int local_irq, int *irqp);
 
-irqreturn_t gsc_asic_intr(int irq, void *dev, struct pt_regs *regs);
+irqreturn_t gsc_asic_intr(int irq, void *dev);
diff --git a/drivers/parisc/power.c b/drivers/parisc/power.c
index 2eb3577..97e9dc0 100644
--- a/drivers/parisc/power.c
+++ b/drivers/parisc/power.c
@@ -188,7 +188,7 @@ static void polling_tasklet_func(unsigned long soft_power_reg)
  * powerfail interruption handler (irq IRQ_FROM_REGION(CPU_IRQ_REGION)+2) 
  */
 #if 0
-static void powerfail_interrupt(int code, void *x, struct pt_regs *regs)
+static void powerfail_interrupt(int code, void *x)
 {
 	printk(KERN_CRIT "POWERFAIL INTERRUPTION !\n");
 	poweroff();
diff --git a/drivers/parisc/superio.c b/drivers/parisc/superio.c
index 4ee26a6..1fd97f7 100644
--- a/drivers/parisc/superio.c
+++ b/drivers/parisc/superio.c
@@ -94,7 +94,7 @@ static struct superio_device sio_dev;
 #define PFX	SUPERIO ": "
 
 static irqreturn_t
-superio_interrupt(int parent_irq, void *devp, struct pt_regs *regs)
+superio_interrupt(int parent_irq, void *devp)
 {
 	u8 results;
 	u8 local_irq;
@@ -138,7 +138,7 @@ superio_interrupt(int parent_irq, void *devp, struct pt_regs *regs)
 	}
 
 	/* Call the appropriate device's interrupt */
-	__do_IRQ(local_irq, regs);
+	__do_IRQ(local_irq);
 
 	/* set EOI - forces a new interrupt if a lower priority device
 	 * still needs service.