powerpc/vdso32: implement clock_getres entirely

clock_getres returns hrtimer_res for all clocks but coarse ones
for which it returns KTIME_LOW_RES.

return EINVAL for unknown clocks.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/37f94e47c91070b7606fb3ec3fe6fd2302a475a0.1575273217.git.christophe.leroy@c-s.fr

arch/powerpc/kernel/asm-offsets.c

@@ -413,7 +413,10 @@ int main(void)
 	DEFINE(CLOCK_MONOTONIC, CLOCK_MONOTONIC);
 	DEFINE(CLOCK_REALTIME_COARSE, CLOCK_REALTIME_COARSE);
 	DEFINE(CLOCK_MONOTONIC_COARSE, CLOCK_MONOTONIC_COARSE);
+	DEFINE(CLOCK_MAX, CLOCK_TAI);
 	DEFINE(NSEC_PER_SEC, NSEC_PER_SEC);
+	DEFINE(EINVAL, EINVAL);
+	DEFINE(KTIME_LOW_RES, KTIME_LOW_RES);
 
 #ifdef CONFIG_BUG
 	DEFINE(BUG_ENTRY_SIZE, sizeof(struct bug_entry));

arch/powerpc/kernel/vdso32/gettimeofday.S

@@ -196,17 +196,20 @@ V_FUNCTION_END(__kernel_clock_gettime)
 V_FUNCTION_BEGIN(__kernel_clock_getres)
   .cfi_startproc
 	/* Check for supported clock IDs */
-	cmpwi	cr0,r3,CLOCK_REALTIME
-	cmpwi	cr1,r3,CLOCK_MONOTONIC
-	cror	cr0*4+eq,cr0*4+eq,cr1*4+eq
-	bne	cr0,99f
+	cmplwi	cr0, r3, CLOCK_MAX
+	cmpwi	cr1, r3, CLOCK_REALTIME_COARSE
+	cmpwi	cr7, r3, CLOCK_MONOTONIC_COARSE
+	bgt	cr0, 99f
+	LOAD_REG_IMMEDIATE(r5, KTIME_LOW_RES)
+	beq	cr1, 1f
+	beq	cr7, 1f
 
 	mflr	r12
   .cfi_register lr,r12
 	get_datapage	r3, r0
 	lwz	r5, CLOCK_HRTIMER_RES(r3)
 	mtlr	r12
-	li	r3,0
+1:	li	r3,0
 	cmpli	cr0,r4,0
 	crclr	cr0*4+so
 	beqlr
@@ -215,11 +218,11 @@ V_FUNCTION_BEGIN(__kernel_clock_getres)
 	blr
 
 	/*
-	 * syscall fallback
+	 * invalid clock
 	 */
 99:
-	li	r0,__NR_clock_getres
-	sc
+	li	r3, EINVAL
+	crset	so
 	blr
   .cfi_endproc
 V_FUNCTION_END(__kernel_clock_getres)