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, 9 insertions, 9 deletions

diff --git a/drivers/pci/hotplug/cpci_hotplug_core.c b/drivers/pci/hotplug/cpci_hotplug_core.c
index d5df587..d06ab40 100644
--- a/drivers/pci/hotplug/cpci_hotplug_core.c
+++ b/drivers/pci/hotplug/cpci_hotplug_core.c
@@ -342,7 +342,7 @@ cpci_hp_unregister_bus(struct pci_bus *bus)
 
 /* This is the interrupt mode interrupt handler */
 static irqreturn_t
-cpci_hp_intr(int irq, void *data, struct pt_regs *regs)
+cpci_hp_intr(int irq, void *data)
 {
 	dbg("entered cpci_hp_intr");
 
diff --git a/drivers/pci/hotplug/cpqphp.h b/drivers/pci/hotplug/cpqphp.h
index c74e9e3..ea040c3 100644
--- a/drivers/pci/hotplug/cpqphp.h
+++ b/drivers/pci/hotplug/cpqphp.h
@@ -409,7 +409,7 @@ extern void cpqhp_remove_debugfs_files		(struct controller *ctrl);
 
 /* controller functions */
 extern void	cpqhp_pushbutton_thread		(unsigned long event_pointer);
-extern irqreturn_t cpqhp_ctrl_intr		(int IRQ, void *data, struct pt_regs *regs);
+extern irqreturn_t cpqhp_ctrl_intr		(int IRQ, void *data);
 extern int	cpqhp_find_available_resources	(struct controller *ctrl, void __iomem *rom_start);
 extern int	cpqhp_event_start_thread	(void);
 extern void	cpqhp_event_stop_thread		(void);
diff --git a/drivers/pci/hotplug/cpqphp_ctrl.c b/drivers/pci/hotplug/cpqphp_ctrl.c
index ae2dd36..3ec2ad7 100644
--- a/drivers/pci/hotplug/cpqphp_ctrl.c
+++ b/drivers/pci/hotplug/cpqphp_ctrl.c
@@ -889,7 +889,7 @@ int cpqhp_resource_sort_and_combine(struct pci_resource **head)
 }
 
 
-irqreturn_t cpqhp_ctrl_intr(int IRQ, void *data, struct pt_regs *regs)
+irqreturn_t cpqhp_ctrl_intr(int IRQ, void *data)
 {
 	struct controller *ctrl = data;
 	u8 schedule_flag = 0;
diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index 6ab3b6c..703a64a 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -222,7 +222,7 @@ static struct php_ctlr_state_s *php_ctlr_list_head; /* HPC state linked list */
 static int ctlr_seq_num = 0;	/* Controller sequence # */
 static spinlock_t list_lock;
 
-static irqreturn_t pcie_isr(int IRQ, void *dev_id, struct pt_regs *regs);
+static irqreturn_t pcie_isr(int IRQ, void *dev_id);
 
 static void start_int_poll_timer(struct php_ctlr_state_s *php_ctlr, int seconds);
 
@@ -239,7 +239,7 @@ static void int_poll_timeout(unsigned long lphp_ctlr)
 	}
 
 	/* Poll for interrupt events.  regs == NULL => polling */
-	pcie_isr( 0, (void *)php_ctlr, NULL );
+	pcie_isr( 0, (void *)php_ctlr );
 
 	init_timer(&php_ctlr->int_poll_timer);
 
@@ -863,7 +863,7 @@ static int hpc_power_off_slot(struct slot * slot)
 	return retval;
 }
 
-static irqreturn_t pcie_isr(int IRQ, void *dev_id, struct pt_regs *regs)
+static irqreturn_t pcie_isr(int IRQ, void *dev_id)
 {
 	struct controller *ctrl = NULL;
 	struct php_ctlr_state_s *php_ctlr;
diff --git a/drivers/pci/hotplug/shpchp_hpc.c b/drivers/pci/hotplug/shpchp_hpc.c
index 0f9798d..4d8aee1 100644
--- a/drivers/pci/hotplug/shpchp_hpc.c
+++ b/drivers/pci/hotplug/shpchp_hpc.c
@@ -218,7 +218,7 @@ static spinlock_t list_lock;
 
 static atomic_t shpchp_num_controllers = ATOMIC_INIT(0);
 
-static irqreturn_t shpc_isr(int irq, void *dev_id, struct pt_regs *regs);
+static irqreturn_t shpc_isr(int irq, void *dev_id);
 static void start_int_poll_timer(struct php_ctlr_state_s *php_ctlr, int sec);
 static int hpc_check_cmd_status(struct controller *ctrl);
 
@@ -276,7 +276,7 @@ static void int_poll_timeout(unsigned long lphp_ctlr)
 	DBG_ENTER_ROUTINE
 
 	/* Poll for interrupt events.  regs == NULL => polling */
-	shpc_isr(0, php_ctlr->callback_instance_id, NULL);
+	shpc_isr(0, php_ctlr->callback_instance_id);
 
 	init_timer(&php_ctlr->int_poll_timer);
 	if (!shpchp_poll_time)
@@ -870,7 +870,7 @@ static int hpc_set_bus_speed_mode(struct slot * slot, enum pci_bus_speed value)
 	return retval;
 }
 
-static irqreturn_t shpc_isr(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t shpc_isr(int irq, void *dev_id)
 {
 	struct controller *ctrl = (struct controller *)dev_id;
 	struct php_ctlr_state_s *php_ctlr = ctrl->hpc_ctlr_handle;