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)

4 files changed, 8 insertions, 12 deletions

diff --git a/drivers/input/joystick/iforce/iforce-packets.c b/drivers/input/joystick/iforce/iforce-packets.c
index 8632d47a7fb..808f05932a6 100644
--- a/drivers/input/joystick/iforce/iforce-packets.c
+++ b/drivers/input/joystick/iforce/iforce-packets.c
@@ -155,7 +155,7 @@ static int mark_core_as_ready(struct iforce *iforce, unsigned short addr)
 	return -1;
 }
 
-void iforce_process_packet(struct iforce *iforce, u16 cmd, unsigned char *data, struct pt_regs *regs)
+void iforce_process_packet(struct iforce *iforce, u16 cmd, unsigned char *data)
 {
 	struct input_dev *dev = iforce->dev;
 	int i;
@@ -183,9 +183,6 @@ void iforce_process_packet(struct iforce *iforce, u16 cmd, unsigned char *data,
 
 		case 0x01:	/* joystick position data */
 		case 0x03:	/* wheel position data */
-
-			input_regs(dev, regs);
-
 			if (HI(cmd) == 1) {
 				input_report_abs(dev, ABS_X, (__s16) (((__s16)data[1] << 8) | data[0]));
 				input_report_abs(dev, ABS_Y, (__s16) (((__s16)data[3] << 8) | data[2]));
@@ -224,7 +221,6 @@ void iforce_process_packet(struct iforce *iforce, u16 cmd, unsigned char *data,
 			break;
 
 		case 0x02:	/* status report */
-			input_regs(dev, regs);
 			input_report_key(dev, BTN_DEAD, data[0] & 0x02);
 			input_sync(dev);
 
diff --git a/drivers/input/joystick/iforce/iforce-serio.c b/drivers/input/joystick/iforce/iforce-serio.c
index 64a78c51548..ca08f45c204 100644
--- a/drivers/input/joystick/iforce/iforce-serio.c
+++ b/drivers/input/joystick/iforce/iforce-serio.c
@@ -81,7 +81,7 @@ static void iforce_serio_write_wakeup(struct serio *serio)
 }
 
 static irqreturn_t iforce_serio_irq(struct serio *serio,
-		unsigned char data, unsigned int flags, struct pt_regs *regs)
+		unsigned char data, unsigned int flags)
 {
 	struct iforce *iforce = serio_get_drvdata(serio);
 
@@ -115,7 +115,7 @@ static irqreturn_t iforce_serio_irq(struct serio *serio,
 	}
 
 	if (iforce->idx == iforce->len) {
-		iforce_process_packet(iforce, (iforce->id << 8) | iforce->idx, iforce->data, regs);
+		iforce_process_packet(iforce, (iforce->id << 8) | iforce->idx, iforce->data);
 		iforce->pkt = 0;
 		iforce->id  = 0;
 		iforce->len = 0;
diff --git a/drivers/input/joystick/iforce/iforce-usb.c b/drivers/input/joystick/iforce/iforce-usb.c
index fe79d158456..105112fb7b5 100644
--- a/drivers/input/joystick/iforce/iforce-usb.c
+++ b/drivers/input/joystick/iforce/iforce-usb.c
@@ -74,7 +74,7 @@ void iforce_usb_xmit(struct iforce *iforce)
 	spin_unlock_irqrestore(&iforce->xmit_lock, flags);
 }
 
-static void iforce_usb_irq(struct urb *urb, struct pt_regs *regs)
+static void iforce_usb_irq(struct urb *urb)
 {
 	struct iforce *iforce = urb->context;
 	int status;
@@ -96,7 +96,7 @@ static void iforce_usb_irq(struct urb *urb, struct pt_regs *regs)
 	}
 
 	iforce_process_packet(iforce,
-		(iforce->data[0] << 8) | (urb->actual_length - 1), iforce->data + 1, regs);
+		(iforce->data[0] << 8) | (urb->actual_length - 1), iforce->data + 1);
 
 exit:
 	status = usb_submit_urb (urb, GFP_ATOMIC);
@@ -105,7 +105,7 @@ exit:
 		     __FUNCTION__, status);
 }
 
-static void iforce_usb_out(struct urb *urb, struct pt_regs *regs)
+static void iforce_usb_out(struct urb *urb)
 {
 	struct iforce *iforce = urb->context;
 
@@ -119,7 +119,7 @@ static void iforce_usb_out(struct urb *urb, struct pt_regs *regs)
 	wake_up(&iforce->wait);
 }
 
-static void iforce_usb_ctrl(struct urb *urb, struct pt_regs *regs)
+static void iforce_usb_ctrl(struct urb *urb)
 {
 	struct iforce *iforce = urb->context;
 	if (urb->status) return;
diff --git a/drivers/input/joystick/iforce/iforce.h b/drivers/input/joystick/iforce/iforce.h
index 947df273984..ffaeaefa1a4 100644
--- a/drivers/input/joystick/iforce/iforce.h
+++ b/drivers/input/joystick/iforce/iforce.h
@@ -160,7 +160,7 @@ void iforce_delete_device(struct iforce *iforce);
 
 /* iforce-packets.c */
 int iforce_control_playback(struct iforce*, u16 id, unsigned int);
-void iforce_process_packet(struct iforce *iforce, u16 cmd, unsigned char *data, struct pt_regs *regs);
+void iforce_process_packet(struct iforce *iforce, u16 cmd, unsigned char *data);
 int iforce_send_packet(struct iforce *iforce, u16 cmd, unsigned char* data);
 void iforce_dump_packet(char *msg, u16 cmd, unsigned char *data) ;
 int iforce_get_id_packet(struct iforce *iforce, char *packet);