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)

7 files changed, 11 insertions, 15 deletions

diff --git a/drivers/rtc/rtc-at91.c b/drivers/rtc/rtc-at91.c
index c0714da..bd61e99 100644
--- a/drivers/rtc/rtc-at91.c
+++ b/drivers/rtc/rtc-at91.c
@@ -238,8 +238,7 @@ static int at91_rtc_proc(struct device *dev, struct seq_file *seq)
 /*
  * IRQ handler for the RTC
  */
-static irqreturn_t at91_rtc_interrupt(int irq, void *dev_id,
-					struct pt_regs *regs)
+static irqreturn_t at91_rtc_interrupt(int irq, void *dev_id)
 {
 	struct platform_device *pdev = dev_id;
 	struct rtc_device *rtc = platform_get_drvdata(pdev);
diff --git a/drivers/rtc/rtc-ds1553.c b/drivers/rtc/rtc-ds1553.c
index 9647188..78552e6 100644
--- a/drivers/rtc/rtc-ds1553.c
+++ b/drivers/rtc/rtc-ds1553.c
@@ -189,8 +189,7 @@ static int ds1553_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
 	return 0;
 }
 
-static irqreturn_t ds1553_rtc_interrupt(int irq, void *dev_id,
-					struct pt_regs *regs)
+static irqreturn_t ds1553_rtc_interrupt(int irq, void *dev_id)
 {
 	struct platform_device *pdev = dev_id;
 	struct rtc_plat_data *pdata = platform_get_drvdata(pdev);
diff --git a/drivers/rtc/rtc-pl031.c b/drivers/rtc/rtc-pl031.c
index 739d1a6..f13daa9 100644
--- a/drivers/rtc/rtc-pl031.c
+++ b/drivers/rtc/rtc-pl031.c
@@ -47,7 +47,7 @@ struct pl031_local {
 	void __iomem *base;
 };
 
-static irqreturn_t pl031_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t pl031_interrupt(int irq, void *dev_id)
 {
 	struct rtc_device *rtc = dev_id;
 
diff --git a/drivers/rtc/rtc-s3c.c b/drivers/rtc/rtc-s3c.c
index 625dad2..e301dea 100644
--- a/drivers/rtc/rtc-s3c.c
+++ b/drivers/rtc/rtc-s3c.c
@@ -46,7 +46,7 @@ static unsigned int tick_count;
 
 /* IRQ Handlers */
 
-static irqreturn_t s3c_rtc_alarmirq(int irq, void *id, struct pt_regs *r)
+static irqreturn_t s3c_rtc_alarmirq(int irq, void *id)
 {
 	struct rtc_device *rdev = id;
 
@@ -54,7 +54,7 @@ static irqreturn_t s3c_rtc_alarmirq(int irq, void *id, struct pt_regs *r)
 	return IRQ_HANDLED;
 }
 
-static irqreturn_t s3c_rtc_tickirq(int irq, void *id, struct pt_regs *r)
+static irqreturn_t s3c_rtc_tickirq(int irq, void *id)
 {
 	struct rtc_device *rdev = id;
 
diff --git a/drivers/rtc/rtc-sa1100.c b/drivers/rtc/rtc-sa1100.c
index 439c41a..bd4d7d1 100644
--- a/drivers/rtc/rtc-sa1100.c
+++ b/drivers/rtc/rtc-sa1100.c
@@ -68,8 +68,7 @@ static int rtc_update_alarm(struct rtc_time *alrm)
 	return ret;
 }
 
-static irqreturn_t sa1100_rtc_interrupt(int irq, void *dev_id,
-		struct pt_regs *regs)
+static irqreturn_t sa1100_rtc_interrupt(int irq, void *dev_id)
 {
 	struct platform_device *pdev = to_platform_device(dev_id);
 	struct rtc_device *rtc = platform_get_drvdata(pdev);
@@ -106,8 +105,7 @@ static irqreturn_t sa1100_rtc_interrupt(int irq, void *dev_id,
 
 static int rtc_timer1_count;
 
-static irqreturn_t timer1_interrupt(int irq, void *dev_id,
-		struct pt_regs *regs)
+static irqreturn_t timer1_interrupt(int irq, void *dev_id)
 {
 	struct platform_device *pdev = to_platform_device(dev_id);
 	struct rtc_device *rtc = platform_get_drvdata(pdev);
diff --git a/drivers/rtc/rtc-sh.c b/drivers/rtc/rtc-sh.c
index d2ce0c8..8b6efcc 100644
--- a/drivers/rtc/rtc-sh.c
+++ b/drivers/rtc/rtc-sh.c
@@ -73,7 +73,7 @@ struct sh_rtc {
 	spinlock_t lock;
 };
 
-static irqreturn_t sh_rtc_interrupt(int irq, void *id, struct pt_regs *regs)
+static irqreturn_t sh_rtc_interrupt(int irq, void *id)
 {
 	struct platform_device *pdev = id;
 	struct sh_rtc *rtc = platform_get_drvdata(pdev);
@@ -97,7 +97,7 @@ static irqreturn_t sh_rtc_interrupt(int irq, void *id, struct pt_regs *regs)
 	return IRQ_HANDLED;
 }
 
-static irqreturn_t sh_rtc_periodic(int irq, void *id, struct pt_regs *regs)
+static irqreturn_t sh_rtc_periodic(int irq, void *id)
 {
 	struct sh_rtc *rtc = dev_get_drvdata(id);
 
diff --git a/drivers/rtc/rtc-vr41xx.c b/drivers/rtc/rtc-vr41xx.c
index 58e5ed0..e40322b 100644
--- a/drivers/rtc/rtc-vr41xx.c
+++ b/drivers/rtc/rtc-vr41xx.c
@@ -268,7 +268,7 @@ static int vr41xx_rtc_ioctl(struct device *dev, unsigned int cmd, unsigned long
 	return 0;
 }
 
-static irqreturn_t elapsedtime_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t elapsedtime_interrupt(int irq, void *dev_id)
 {
 	struct platform_device *pdev = (struct platform_device *)dev_id;
 	struct rtc_device *rtc = platform_get_drvdata(pdev);
@@ -280,7 +280,7 @@ static irqreturn_t elapsedtime_interrupt(int irq, void *dev_id, struct pt_regs *
 	return IRQ_HANDLED;
 }
 
-static irqreturn_t rtclong1_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t rtclong1_interrupt(int irq, void *dev_id)
 {
 	struct platform_device *pdev = (struct platform_device *)dev_id;
 	struct rtc_device *rtc = platform_get_drvdata(pdev);