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)

1 files changed, 15 insertions, 15 deletions

diff --git a/drivers/usb/misc/auerswald.c b/drivers/usb/misc/auerswald.c
index 4fd2110b3411..0be9d62d62ae 100644
--- a/drivers/usb/misc/auerswald.c
+++ b/drivers/usb/misc/auerswald.c
@@ -267,7 +267,7 @@ typedef struct
 
 /*-------------------------------------------------------------------*/
 /* Forwards */
-static void auerswald_ctrlread_complete (struct urb * urb, struct pt_regs *regs);
+static void auerswald_ctrlread_complete (struct urb * urb);
 static void auerswald_removeservice (pauerswald_t cp, pauerscon_t scp);
 static struct usb_driver auerswald_driver;
 
@@ -277,7 +277,7 @@ static struct usb_driver auerswald_driver;
 /* --------------------------                                        */
 
 /* completion function for chained urbs */
-static void auerchain_complete (struct urb * urb, struct pt_regs *regs)
+static void auerchain_complete (struct urb * urb)
 {
 	unsigned long flags;
         int result;
@@ -296,7 +296,7 @@ static void auerchain_complete (struct urb * urb, struct pt_regs *regs)
            NOTE: this function may lead to more urbs submitted into the chain.
                  (no chain lock at calling complete()!)
                  acp->active != NULL is protecting us against recursion.*/
-        urb->complete (urb, regs);
+        urb->complete (urb);
 
         /* detach element from chain data structure */
 	spin_lock_irqsave (&acp->lock, flags);
@@ -331,7 +331,7 @@ static void auerchain_complete (struct urb * urb, struct pt_regs *regs)
                         urb->status = result;
                         dbg("auerchain_complete: usb_submit_urb with error code %d", result);
                         /* and do error handling via *this* completion function (recursive) */
-                        auerchain_complete( urb, NULL);
+                        auerchain_complete( urb);
                 }
         } else {
                 /* simple return without submitting a new urb.
@@ -408,7 +408,7 @@ static int auerchain_submit_urb_list (pauerchain_t acp, struct urb * urb, int ea
                         urb->status = result;
                         dbg("auerchain_submit_urb: usb_submit_urb with error code %d", result);
                         /* and do error handling via completion function */
-                        auerchain_complete( urb, NULL);
+                        auerchain_complete( urb);
                 }
         }
 
@@ -448,7 +448,7 @@ static int auerchain_unlink_urb (pauerchain_t acp, struct urb * urb)
                         spin_unlock_irqrestore (&acp->lock, flags);
                         dbg ("unlink waiting urb");
                         urb->status = -ENOENT;
-                        urb->complete (urb, NULL);
+                        urb->complete (urb);
                         return 0;
                 }
         }
@@ -505,7 +505,7 @@ static void auerchain_unlink_all (pauerchain_t acp)
                 spin_unlock_irqrestore (&acp->lock, flags);
                 dbg ("unlink waiting urb");
                 urbp->status = -ENOENT;
-                urbp->complete (urbp, NULL);
+                urbp->complete (urbp);
                 spin_lock_irqsave (&acp->lock, flags);
         }
         spin_unlock_irqrestore (&acp->lock, flags);
@@ -591,7 +591,7 @@ ac_fail:/* free the elements */
 
 
 /* completion handler for synchronous chained URBs */
-static void auerchain_blocking_completion (struct urb *urb, struct pt_regs *regs)
+static void auerchain_blocking_completion (struct urb *urb)
 {
 	pauerchain_chs_t pchs = (pauerchain_chs_t)urb->context;
 	pchs->done = 1;
@@ -846,7 +846,7 @@ static int auerswald_status_retry (int status)
 }
 
 /* Completion of asynchronous write block */
-static void auerchar_ctrlwrite_complete (struct urb * urb, struct pt_regs *regs)
+static void auerchar_ctrlwrite_complete (struct urb * urb)
 {
 	pauerbuf_t bp = (pauerbuf_t) urb->context;
 	pauerswald_t cp = ((pauerswald_t)((char *)(bp->list)-(unsigned long)(&((pauerswald_t)0)->bufctl)));
@@ -859,7 +859,7 @@ static void auerchar_ctrlwrite_complete (struct urb * urb, struct pt_regs *regs)
 }
 
 /* Completion handler for dummy retry packet */
-static void auerswald_ctrlread_wretcomplete (struct urb * urb, struct pt_regs *regs)
+static void auerswald_ctrlread_wretcomplete (struct urb * urb)
 {
         pauerbuf_t bp = (pauerbuf_t) urb->context;
         pauerswald_t cp;
@@ -893,12 +893,12 @@ static void auerswald_ctrlread_wretcomplete (struct urb * urb, struct pt_regs *r
         if (ret) {
         	dbg ("auerswald_ctrlread_complete: nonzero result of auerchain_submit_urb_list %d", ret);
         	bp->urbp->status = ret;
-        	auerswald_ctrlread_complete (bp->urbp, NULL);
+        	auerswald_ctrlread_complete (bp->urbp);
     	}
 }
 
 /* completion handler for receiving of control messages */
-static void auerswald_ctrlread_complete (struct urb * urb, struct pt_regs *regs)
+static void auerswald_ctrlread_complete (struct urb * urb)
 {
         unsigned int  serviceid;
         pauerswald_t  cp;
@@ -941,7 +941,7 @@ static void auerswald_ctrlread_complete (struct urb * urb, struct pt_regs *regs)
        		if (ret) {
                		dbg ("auerswald_ctrlread_complete: nonzero result of auerchain_submit_urb_list %d", ret);
                		bp->urbp->status = ret;
-               		auerswald_ctrlread_wretcomplete (bp->urbp, regs);
+               		auerswald_ctrlread_wretcomplete (bp->urbp);
 		}
                 return;
         }
@@ -970,7 +970,7 @@ static void auerswald_ctrlread_complete (struct urb * urb, struct pt_regs *regs)
    messages from the USB device.
 */
 /* int completion handler. */
-static void auerswald_int_complete (struct urb * urb, struct pt_regs *regs)
+static void auerswald_int_complete (struct urb * urb)
 {
         unsigned long flags;
         unsigned  int channelid;
@@ -1070,7 +1070,7 @@ static void auerswald_int_complete (struct urb * urb, struct pt_regs *regs)
         if (ret) {
                 dbg ("auerswald_int_complete: nonzero result of auerchain_submit_urb %d", ret);
                 bp->urbp->status = ret;
-                auerswald_ctrlread_complete( bp->urbp, NULL);
+                auerswald_ctrlread_complete( bp->urbp);
 		/* here applies the same problem as above: device locking! */
         }
 exit: