Commit 13371731 authored by Chris Metcalf's avatar Chris Metcalf
Browse files

arch/tile: fix __ndelay etc to work better 



The current implementations of __ndelay and __udelay call a hypervisor
service to delay, but the hypervisor service isn't actually implemented
very well, and the consensus is that Linux should handle figuring this
out natively and not use a hypervisor service.

By converting nanoseconds to cycles, and then spinning until the
cycle counter reaches the desired cycle, we get several benefits:
first, we are sensitive to the actual clock speed; second, we use
less power by issuing a slow SPR read once every six cycles while
we delay; and third, we properly handle the case of an interrupt by
exiting at the target time rather than after some number of cycles.

Signed-off-by: default avatarChris Metcalf <cmetcalf@tilera.com>
parent 04f7a3f1

arch/tile/include/asm/timex.h

+3 −0
Original line number Diff line number Diff line
@@ -38,6 +38,9 @@ static inline cycles_t get_cycles(void) 


cycles_t get_clock_rate(void);



/* Convert nanoseconds to core clock cycles. */

cycles_t ns2cycles(unsigned long nsecs);



/* Called at cpu initialization to set some low-level constants. */

void setup_clock(void);

arch/tile/include/hv/hypervisor.h

+5 −0
Original line number Diff line number Diff line
@@ -963,6 +963,11 @@ HV_ASIDRange hv_inquire_asid(int idx); 




/** Waits for at least the specified number of nanoseconds then returns.

 *

 * NOTE: this deprecated function currently assumes a 750 MHz clock,

 * and is thus not generally suitable for use.  New code should call

 * hv_sysconf(HV_SYSCONF_CPU_SPEED), compute a cycle count to wait for,

 * and delay by looping while checking the cycle counter SPR.

 *

 * @param nanosecs The number of nanoseconds to sleep.

 */

arch/tile/kernel/entry.S

+0 −6
Original line number Diff line number Diff line
@@ -38,12 +38,6 @@ STD_ENTRY(kernel_execve) 
	jrp lr

	STD_ENDPROC(kernel_execve)



/* Delay a fixed number of cycles. */

STD_ENTRY(__delay)

	{ addi r0, r0, -1; bnzt r0, . }

	jrp lr

	STD_ENDPROC(__delay)



/*

 * We don't run this function directly, but instead copy it to a page

 * we map into every user process.  See vdso_setup().

arch/tile/kernel/time.c

+10 −0
Original line number Diff line number Diff line
@@ -224,3 +224,13 @@ int setup_profiling_timer(unsigned int multiplier) 
{

	return -EINVAL;

}



/*

 * Use the tile timer to convert nsecs to core clock cycles, relying

 * on it having the same frequency as SPR_CYCLE.

 */

cycles_t ns2cycles(unsigned long nsecs)

{

	struct clock_event_device *dev = &__get_cpu_var(tile_timer);

	return ((u64)nsecs * dev->mult) >> dev->shift;

}

arch/tile/lib/delay.c

+16 −5
Original line number Diff line number Diff line
@@ -15,20 +15,31 @@ 
#include <linux/module.h>

#include <linux/delay.h>

#include <linux/thread_info.h>

#include <asm/fixmap.h>

#include <hv/hypervisor.h>

#include <asm/timex.h>



void __udelay(unsigned long usecs)

{

	hv_nanosleep(usecs * 1000);

	if (usecs > ULONG_MAX / 1000) {

		WARN_ON_ONCE(usecs > ULONG_MAX / 1000);

		usecs = ULONG_MAX / 1000;

	}

	__ndelay(usecs * 1000);

}

EXPORT_SYMBOL(__udelay);



void __ndelay(unsigned long nsecs)

{

	hv_nanosleep(nsecs);

	cycles_t target = get_cycles();

	target += ns2cycles(nsecs);

	while (get_cycles() < target)

		cpu_relax();

}

EXPORT_SYMBOL(__ndelay);



/* FIXME: should be declared in a header somewhere. */

void __delay(unsigned long cycles)

{

	cycles_t target = get_cycles() + cycles;

	while (get_cycles() < target)

		cpu_relax();

}

EXPORT_SYMBOL(__delay);

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