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, 9 insertions, 9 deletions

diff --git a/drivers/net/hamradio/baycom_epp.c b/drivers/net/hamradio/baycom_epp.c
index 9220de9f4fe..1ed9cccd3c1 100644
--- a/drivers/net/hamradio/baycom_epp.c
+++ b/drivers/net/hamradio/baycom_epp.c
@@ -323,7 +323,7 @@ static int eppconfig(struct baycom_state *bc)
 
 /* ---------------------------------------------------------------------- */
 
-static void epp_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+static void epp_interrupt(int irq, void *dev_id)
 {
 }
 
diff --git a/drivers/net/hamradio/baycom_par.c b/drivers/net/hamradio/baycom_par.c
index 77411a00d1e..5930aeb3501 100644
--- a/drivers/net/hamradio/baycom_par.c
+++ b/drivers/net/hamradio/baycom_par.c
@@ -270,7 +270,7 @@ static __inline__ void par96_rx(struct net_device *dev, struct baycom_state *bc)
 
 /* --------------------------------------------------------------------- */
 
-static void par96_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+static void par96_interrupt(int irq, void *dev_id)
 {
 	struct net_device *dev = (struct net_device *)dev_id;
 	struct baycom_state *bc = netdev_priv(dev);
diff --git a/drivers/net/hamradio/baycom_ser_fdx.c b/drivers/net/hamradio/baycom_ser_fdx.c
index 55906c7b4bb..59214e74b9c 100644
--- a/drivers/net/hamradio/baycom_ser_fdx.c
+++ b/drivers/net/hamradio/baycom_ser_fdx.c
@@ -279,7 +279,7 @@ static __inline__ void ser12_rx(struct net_device *dev, struct baycom_state *bc,
 
 /* --------------------------------------------------------------------- */
 
-static irqreturn_t ser12_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t ser12_interrupt(int irq, void *dev_id)
 {
 	struct net_device *dev = (struct net_device *)dev_id;
 	struct baycom_state *bc = netdev_priv(dev);
diff --git a/drivers/net/hamradio/baycom_ser_hdx.c b/drivers/net/hamradio/baycom_ser_hdx.c
index de95de8983d..3bcc57acbe6 100644
--- a/drivers/net/hamradio/baycom_ser_hdx.c
+++ b/drivers/net/hamradio/baycom_ser_hdx.c
@@ -373,7 +373,7 @@ static inline void ser12_rx(struct net_device *dev, struct baycom_state *bc)
 
 /* --------------------------------------------------------------------- */
 
-static irqreturn_t ser12_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t ser12_interrupt(int irq, void *dev_id)
 {
 	struct net_device *dev = (struct net_device *)dev_id;
 	struct baycom_state *bc = netdev_priv(dev);
diff --git a/drivers/net/hamradio/dmascc.c b/drivers/net/hamradio/dmascc.c
index c9a46b89942..0f8b9afd55b 100644
--- a/drivers/net/hamradio/dmascc.c
+++ b/drivers/net/hamradio/dmascc.c
@@ -249,7 +249,7 @@ static void start_timer(struct scc_priv *priv, int t, int r15);
 static inline unsigned char random(void);
 
 static inline void z8530_isr(struct scc_info *info);
-static irqreturn_t scc_isr(int irq, void *dev_id, struct pt_regs *regs);
+static irqreturn_t scc_isr(int irq, void *dev_id);
 static void rx_isr(struct scc_priv *priv);
 static void special_condition(struct scc_priv *priv, int rc);
 static void rx_bh(void *arg);
@@ -1142,7 +1142,7 @@ static inline void z8530_isr(struct scc_info *info)
 }
 
 
-static irqreturn_t scc_isr(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t scc_isr(int irq, void *dev_id)
 {
 	struct scc_info *info = dev_id;
 
diff --git a/drivers/net/hamradio/scc.c b/drivers/net/hamradio/scc.c
index df4b68142ac..ec9b6d9b6f0 100644
--- a/drivers/net/hamradio/scc.c
+++ b/drivers/net/hamradio/scc.c
@@ -200,7 +200,7 @@ static void z8530_init(void);
 
 static void init_channel(struct scc_channel *scc);
 static void scc_key_trx (struct scc_channel *scc, char tx);
-static irqreturn_t scc_isr(int irq, void *dev_id, struct pt_regs *regs);
+static irqreturn_t scc_isr(int irq, void *dev_id);
 static void scc_init_timer(struct scc_channel *scc);
 
 static int scc_net_alloc(const char *name, struct scc_channel *scc);
@@ -626,7 +626,7 @@ static void scc_isr_dispatch(struct scc_channel *scc, int vector)
 
 #define SCC_IRQTIMEOUT 30000
 
-static irqreturn_t scc_isr(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t scc_isr(int irq, void *dev_id)
 {
 	unsigned char vector;	
 	struct scc_channel *scc;
diff --git a/drivers/net/hamradio/yam.c b/drivers/net/hamradio/yam.c
index f98f5777dfb..3c4455bd466 100644
--- a/drivers/net/hamradio/yam.c
+++ b/drivers/net/hamradio/yam.c
@@ -702,7 +702,7 @@ static void yam_tx_byte(struct net_device *dev, struct yam_port *yp)
 * ISR routine
 ************************************************************************************/
 
-static irqreturn_t yam_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t yam_interrupt(int irq, void *dev_id)
 {
 	struct net_device *dev;
 	struct yam_port *yp;