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, 8 insertions, 11 deletions

diff --git a/drivers/isdn/hardware/avm/avmcard.h b/drivers/isdn/hardware/avm/avmcard.h
index 3b431723c7c..d964f07e4a5 100644
--- a/drivers/isdn/hardware/avm/avmcard.h
+++ b/drivers/isdn/hardware/avm/avmcard.h
@@ -554,7 +554,7 @@ void b1_register_appl(struct capi_ctr *ctrl, u16 appl,
 void b1_release_appl(struct capi_ctr *ctrl, u16 appl);
 u16  b1_send_message(struct capi_ctr *ctrl, struct sk_buff *skb);
 void b1_parse_version(avmctrl_info *card);
-irqreturn_t b1_interrupt(int interrupt, void *devptr, struct pt_regs *regs);
+irqreturn_t b1_interrupt(int interrupt, void *devptr);
 
 int b1ctl_read_proc(char *page, char **start, off_t off,
                         int count, int *eof, struct capi_ctr *ctrl);
@@ -567,7 +567,7 @@ void avmcard_dma_free(avmcard_dmainfo *);
 int b1pciv4_detect(avmcard *card);
 int t1pci_detect(avmcard *card);
 void b1dma_reset(avmcard *card);
-irqreturn_t b1dma_interrupt(int interrupt, void *devptr, struct pt_regs *regs);
+irqreturn_t b1dma_interrupt(int interrupt, void *devptr);
 
 int b1dma_load_firmware(struct capi_ctr *ctrl, capiloaddata *data);
 void b1dma_reset_ctr(struct capi_ctr *ctrl);
diff --git a/drivers/isdn/hardware/avm/b1.c b/drivers/isdn/hardware/avm/b1.c
index 0c7061d5502..da272924771 100644
--- a/drivers/isdn/hardware/avm/b1.c
+++ b/drivers/isdn/hardware/avm/b1.c
@@ -485,7 +485,7 @@ void b1_parse_version(avmctrl_info *cinfo)
 
 /* ------------------------------------------------------------- */
 
-irqreturn_t b1_interrupt(int interrupt, void *devptr, struct pt_regs *regs)
+irqreturn_t b1_interrupt(int interrupt, void *devptr)
 {
         avmcard *card = devptr;
         avmctrl_info *cinfo = &card->ctrlinfo[0];
diff --git a/drivers/isdn/hardware/avm/b1dma.c b/drivers/isdn/hardware/avm/b1dma.c
index a4beeb46c85..ddd47cdfdb1 100644
--- a/drivers/isdn/hardware/avm/b1dma.c
+++ b/drivers/isdn/hardware/avm/b1dma.c
@@ -628,7 +628,7 @@ static void b1dma_handle_interrupt(avmcard *card)
         spin_unlock(&card->lock);
 }
 
-irqreturn_t b1dma_interrupt(int interrupt, void *devptr, struct pt_regs *regs)
+irqreturn_t b1dma_interrupt(int interrupt, void *devptr)
 {
         avmcard *card = devptr;
 
diff --git a/drivers/isdn/hardware/avm/c4.c b/drivers/isdn/hardware/avm/c4.c
index 6c3d5f5f1f4..2a3eb38f0eb 100644
--- a/drivers/isdn/hardware/avm/c4.c
+++ b/drivers/isdn/hardware/avm/c4.c
@@ -713,7 +713,7 @@ static irqreturn_t c4_handle_interrupt(avmcard *card)
         return IRQ_HANDLED;
 }
 
-static irqreturn_t c4_interrupt(int interrupt, void *devptr, struct pt_regs *regs)
+static irqreturn_t c4_interrupt(int interrupt, void *devptr)
 {
         avmcard *card = devptr;
 
diff --git a/drivers/isdn/hardware/avm/t1isa.c b/drivers/isdn/hardware/avm/t1isa.c
index 5a2f854d55b..e47c60b0a8e 100644
--- a/drivers/isdn/hardware/avm/t1isa.c
+++ b/drivers/isdn/hardware/avm/t1isa.c
@@ -131,7 +131,7 @@ static int t1_detectandinit(unsigned int base, unsigned irq, int cardnr)
         return 0;
 }
 
-static irqreturn_t t1isa_interrupt(int interrupt, void *devptr, struct pt_regs *regs)
+static irqreturn_t t1isa_interrupt(int interrupt, void *devptr)
 {
         avmcard *card = devptr;
         avmctrl_info *cinfo = &card->ctrlinfo[0];
diff --git a/drivers/isdn/hardware/eicon/diva.c b/drivers/isdn/hardware/eicon/diva.c
index 8ab8027f33c..ffa2afa77c2 100644
--- a/drivers/isdn/hardware/eicon/diva.c
+++ b/drivers/isdn/hardware/eicon/diva.c
@@ -71,8 +71,6 @@ DivaIdiReqFunc(29)
 DivaIdiReqFunc(30)
 DivaIdiReqFunc(31)
 
-struct pt_regs;
-
 /*
 **  LOCALS
 */
@@ -515,7 +513,7 @@ diva_xdi_read(void *adapter, void *os_handle, void __user *dst,
 }
 
 
-irqreturn_t diva_os_irq_wrapper(int irq, void *context, struct pt_regs *regs)
+irqreturn_t diva_os_irq_wrapper(int irq, void *context)
 {
         diva_os_xdi_adapter_t *a = (diva_os_xdi_adapter_t *) context;
         diva_xdi_clear_interrupts_proc_t clear_int_proc;
diff --git a/drivers/isdn/hardware/eicon/divasmain.c b/drivers/isdn/hardware/eicon/divasmain.c
index b7dadba13e8..dae2e83dd5e 100644
--- a/drivers/isdn/hardware/eicon/divasmain.c
+++ b/drivers/isdn/hardware/eicon/divasmain.c
@@ -58,8 +58,7 @@ static char *DRIVERLNAME = "divas";
 static char *DEVNAME = "Divas";
 char *DRIVERRELEASE_DIVAS = "2.0";
 
-extern irqreturn_t diva_os_irq_wrapper(int irq, void *context,
-                                struct pt_regs *regs);
+extern irqreturn_t diva_os_irq_wrapper(int irq, void *context);
 extern int create_divas_proc(void);
 extern void remove_divas_proc(void);
 extern void diva_get_vserial_number(PISDN_ADAPTER IoAdapter, char *buf);