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)

5 files changed, 6 insertions, 10 deletions

diff --git a/sound/drivers/mpu401/mpu401_uart.c b/sound/drivers/mpu401/mpu401_uart.c
index 4bf07ca9b17d..3daa9fa56c0b 100644
--- a/sound/drivers/mpu401/mpu401_uart.c
+++ b/sound/drivers/mpu401/mpu401_uart.c
@@ -125,12 +125,10 @@ static void _snd_mpu401_uart_interrupt(struct snd_mpu401 *mpu)
  * snd_mpu401_uart_interrupt - generic MPU401-UART interrupt handler
  * @irq: the irq number
  * @dev_id: mpu401 instance
- * @regs: the reigster
  *
  * Processes the interrupt for MPU401-UART i/o.
  */
-irqreturn_t snd_mpu401_uart_interrupt(int irq, void *dev_id,
-				      struct pt_regs *regs)
+irqreturn_t snd_mpu401_uart_interrupt(int irq, void *dev_id)
 {
 	struct snd_mpu401 *mpu = dev_id;
 	
@@ -146,12 +144,10 @@ EXPORT_SYMBOL(snd_mpu401_uart_interrupt);
  * snd_mpu401_uart_interrupt_tx - generic MPU401-UART transmit irq handler
  * @irq: the irq number
  * @dev_id: mpu401 instance
- * @regs: the reigster
  *
  * Processes the interrupt for MPU401-UART output.
  */
-irqreturn_t snd_mpu401_uart_interrupt_tx(int irq, void *dev_id,
-					 struct pt_regs *regs)
+irqreturn_t snd_mpu401_uart_interrupt_tx(int irq, void *dev_id)
 {
 	struct snd_mpu401 *mpu = dev_id;
 	
diff --git a/sound/drivers/mtpav.c b/sound/drivers/mtpav.c
index e064d6c5685b..a9ff391258e7 100644
--- a/sound/drivers/mtpav.c
+++ b/sound/drivers/mtpav.c
@@ -570,7 +570,7 @@ static void snd_mtpav_read_bytes(struct mtpav *mcrd)
 	} while (sbyt & SIGS_BYTE);
 }
 
-static irqreturn_t snd_mtpav_irqh(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t snd_mtpav_irqh(int irq, void *dev_id)
 {
 	struct mtpav *mcard = dev_id;
 
diff --git a/sound/drivers/mts64.c b/sound/drivers/mts64.c
index ab8d4effcf9e..5327c6f841f4 100644
--- a/sound/drivers/mts64.c
+++ b/sound/drivers/mts64.c
@@ -838,7 +838,7 @@ static int __devinit snd_mts64_rawmidi_create(struct snd_card *card)
 /*********************************************************************
  * parport stuff
  *********************************************************************/
-static void snd_mts64_interrupt(int irq, void *private, struct pt_regs *r)
+static void snd_mts64_interrupt(int irq, void *private)
 {
 	struct mts64 *mts = ((struct snd_card*)private)->private_data;
 	u16 ret;
diff --git a/sound/drivers/serial-u16550.c b/sound/drivers/serial-u16550.c
index 52afb4bd2079..74028b2219c2 100644
--- a/sound/drivers/serial-u16550.c
+++ b/sound/drivers/serial-u16550.c
@@ -292,7 +292,7 @@ static void snd_uart16550_io_loop(snd_uart16550_t * uart)
  * Note that some devices need OUT2 to be set before they will generate
  * interrupts at all. (Possibly tied to an internal pull-up on CTS?)
  */
-static irqreturn_t snd_uart16550_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t snd_uart16550_interrupt(int irq, void *dev_id)
 {
 	snd_uart16550_t *uart;
 
diff --git a/sound/drivers/vx/vx_core.c b/sound/drivers/vx/vx_core.c
index a60168268ddd..ed19bc17400b 100644
--- a/sound/drivers/vx/vx_core.c
+++ b/sound/drivers/vx/vx_core.c
@@ -537,7 +537,7 @@ static void vx_interrupt(unsigned long private_data)
 /**
  * snd_vx_irq_handler - interrupt handler
  */
-irqreturn_t snd_vx_irq_handler(int irq, void *dev, struct pt_regs *regs)
+irqreturn_t snd_vx_irq_handler(int irq, void *dev)
 {
 	struct vx_core *chip = dev;