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, 14 insertions, 18 deletions

diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index 3f509beb88e..2c9c9462d89 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -304,7 +304,7 @@ static void snoop_urb(struct urb *urb, void __user *userurb)
         printk("\n");
 }
 
-static void async_completed(struct urb *urb, struct pt_regs *regs)
+static void async_completed(struct urb *urb)
 {
         struct async *as = urb->context;
         struct dev_state *ps = as->ps;
diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index e658089f7b5..afa2dd20332 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -522,7 +522,7 @@ error:
         if (urb->status == -EINPROGRESS)
                 urb->status = status;
         spin_unlock (&urb->lock);
-        usb_hcd_giveback_urb (hcd, urb, NULL);
+        usb_hcd_giveback_urb (hcd, urb);
         local_irq_restore (flags);
         return 0;
 }
@@ -572,7 +572,7 @@ void usb_hcd_poll_rh_status(struct usb_hcd *hcd)
 
                 /* local irqs are always blocked in completions */
                 if (length > 0)
-                        usb_hcd_giveback_urb (hcd, urb, NULL);
+                        usb_hcd_giveback_urb (hcd, urb);
                 else
                         hcd->poll_pending = 1;
                 local_irq_restore (flags);
@@ -656,7 +656,7 @@ static int usb_rh_urb_dequeue (struct usb_hcd *hcd, struct urb *urb)
                         urb = NULL;             /* wasn't fully queued */
                 spin_unlock (&hcd_root_hub_lock);
                 if (urb)
-                        usb_hcd_giveback_urb (hcd, urb, NULL);
+                        usb_hcd_giveback_urb (hcd, urb);
                 local_irq_restore (flags);
         }
 
@@ -1498,7 +1498,6 @@ EXPORT_SYMBOL (usb_bus_start_enum);
  * usb_hcd_giveback_urb - return URB from HCD to device driver
  * @hcd: host controller returning the URB
  * @urb: urb being returned to the USB device driver.
- * @regs: pt_regs, passed down to the URB completion handler
  * Context: in_interrupt()
  *
  * This hands the URB from HCD to its USB device driver, using its
@@ -1507,7 +1506,7 @@ EXPORT_SYMBOL (usb_bus_start_enum);
  * the device driver won't cause problems if it frees, modifies,
  * or resubmits this URB.
  */
-void usb_hcd_giveback_urb (struct usb_hcd *hcd, struct urb *urb, struct pt_regs *regs)
+void usb_hcd_giveback_urb (struct usb_hcd *hcd, struct urb *urb)
 {
         int at_root_hub;
 
@@ -1534,7 +1533,7 @@ void usb_hcd_giveback_urb (struct usb_hcd *hcd, struct urb *urb, struct pt_regs
 
         usbmon_urb_complete (&hcd->self, urb);
         /* pass ownership to the completion handler */
-        urb->complete (urb, regs);
+        urb->complete (urb);
         atomic_dec (&urb->use_count);
         if (unlikely (urb->reject))
                 wake_up (&usb_kill_urb_queue);
@@ -1553,7 +1552,7 @@ EXPORT_SYMBOL (usb_hcd_giveback_urb);
  * If the controller isn't HALTed, calls the driver's irq handler.
  * Checks whether the controller is now dead.
  */
-irqreturn_t usb_hcd_irq (int irq, void *__hcd, struct pt_regs * r)
+irqreturn_t usb_hcd_irq (int irq, void *__hcd)
 {
         struct usb_hcd          *hcd = __hcd;
         int                     start = hcd->state;
@@ -1561,7 +1560,7 @@ irqreturn_t usb_hcd_irq (int irq, void *__hcd, struct pt_regs * r)
         if (unlikely(start == HC_STATE_HALT ||
             !test_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags)))
                 return IRQ_NONE;
-        if (hcd->driver->irq (hcd, r) == IRQ_NONE)
+        if (hcd->driver->irq (hcd) == IRQ_NONE)
                 return IRQ_NONE;
 
         set_bit(HCD_FLAG_SAW_IRQ, &hcd->flags);
diff --git a/drivers/usb/core/hcd.h b/drivers/usb/core/hcd.h
index 676877c15f8..8f8df0d4382 100644
--- a/drivers/usb/core/hcd.h
+++ b/drivers/usb/core/hcd.h
@@ -143,15 +143,13 @@ struct hcd_timeout {	/* timeouts we allocate */
 /*-------------------------------------------------------------------------*/
 
 
-struct pt_regs;
-
 struct hc_driver {
         const char      *description;   /* "ehci-hcd" etc */
         const char      *product_desc;  /* product/vendor string */
         size_t          hcd_priv_size;  /* size of private data */
 
         /* irq handler */
-        irqreturn_t     (*irq) (struct usb_hcd *hcd, struct pt_regs *regs);
+        irqreturn_t     (*irq) (struct usb_hcd *hcd);
 
         int     flags;
 #define HCD_MEMORY      0x0001          /* HC regs use memory (else I/O) */
@@ -205,8 +203,7 @@ struct hc_driver {
 
 extern int usb_hcd_submit_urb (struct urb *urb, gfp_t mem_flags);
 extern int usb_hcd_unlink_urb (struct urb *urb, int status);
-extern void usb_hcd_giveback_urb (struct usb_hcd *hcd, struct urb *urb,
-                struct pt_regs *regs);
+extern void usb_hcd_giveback_urb (struct usb_hcd *hcd, struct urb *urb);
 extern void usb_hcd_endpoint_disable (struct usb_device *udev,
                 struct usb_host_endpoint *ep);
 extern int usb_hcd_get_frame_number (struct usb_device *udev);
@@ -248,7 +245,7 @@ void hcd_buffer_free (struct usb_bus *bus, size_t size,
         void *addr, dma_addr_t dma);
 
 /* generic bus glue, needed for host controllers that don't use PCI */
-extern irqreturn_t usb_hcd_irq (int irq, void *__hcd, struct pt_regs *r);
+extern irqreturn_t usb_hcd_irq (int irq, void *__hcd);
 
 extern void usb_hc_died (struct usb_hcd *hcd);
 extern void usb_hcd_poll_rh_status(struct usb_hcd *hcd);
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 7676690a038..66bff184a30 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -291,7 +291,7 @@ void usb_kick_khubd(struct usb_device *hdev)
 
 
 /* completion function, fires on port status changes and various faults */
-static void hub_irq(struct urb *urb, struct pt_regs *regs)
+static void hub_irq(struct urb *urb)
 {
         struct usb_hub *hub = urb->context;
         int status;
diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index 85b1cd18336..fccd1952bad 100644
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -17,7 +17,7 @@
 #include "hcd.h"        /* for usbcore internals */
 #include "usb.h"
 
-static void usb_api_blocking_completion(struct urb *urb, struct pt_regs *regs)
+static void usb_api_blocking_completion(struct urb *urb)
 {
         complete((struct completion *)urb->context);
 }
@@ -246,7 +246,7 @@ static void sg_clean (struct usb_sg_request *io)
         io->dev = NULL;
 }
 
-static void sg_complete (struct urb *urb, struct pt_regs *regs)
+static void sg_complete (struct urb *urb)
 {
         struct usb_sg_request   *io = urb->context;