clocksource/drivers/arm_arch_timer: Move MMIO timer programming over to CVAL

Similarily to the sysreg-based timer, move the MMIO over to using
the CVAL registers instead of TVAL. Note that there is no warranty
that the 64bit MMIO access will be atomic, but the timer is always
disabled at the point where we program CVAL.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211017124225.3018098-8-maz@kernel.org
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

arch/arm/include/asm/arch_timer.h

@@ -7,6 +7,7 @@
 #include <asm/hwcap.h>
 #include <linux/clocksource.h>
 #include <linux/init.h>
+#include <linux/io-64-nonatomic-lo-hi.h>
 #include <linux/types.h>
 
 #include <clocksource/arm_arch_timer.h>

drivers/clocksource/arm_arch_timer.c

@@ -44,11 +44,13 @@
 #define CNTACR_RWVT	BIT(4)
 #define CNTACR_RWPT	BIT(5)
 
-#define CNTVCT_LO	0x08
-#define CNTVCT_HI	0x0c
+#define CNTVCT_LO	0x00
+#define CNTPCT_LO	0x08
 #define CNTFRQ		0x10
+#define CNTP_CVAL_LO	0x20
 #define CNTP_TVAL	0x28
 #define CNTP_CTL	0x2c
+#define CNTV_CVAL_LO	0x30
 #define CNTV_TVAL	0x38
 #define CNTV_CTL	0x3c
 
@@ -112,6 +114,13 @@ void arch_timer_reg_write(int access, enum arch_timer_reg reg, u64 val,
 		case ARCH_TIMER_REG_TVAL:
 			writel_relaxed((u32)val, timer->base + CNTP_TVAL);
 			break;
+		case ARCH_TIMER_REG_CVAL:
+			/*
+			 * Not guaranteed to be atomic, so the timer
+			 * must be disabled at this point.
+			 */
+			writeq_relaxed(val, timer->base + CNTP_CVAL_LO);
+			break;
 		default:
 			BUILD_BUG();
 		}
@@ -124,6 +133,10 @@ void arch_timer_reg_write(int access, enum arch_timer_reg reg, u64 val,
 		case ARCH_TIMER_REG_TVAL:
 			writel_relaxed((u32)val, timer->base + CNTV_TVAL);
 			break;
+		case ARCH_TIMER_REG_CVAL:
+			/* Same restriction as above */
+			writeq_relaxed(val, timer->base + CNTV_CVAL_LO);
+			break;
 		default:
 			BUILD_BUG();
 		}
@@ -720,15 +733,36 @@ static int arch_timer_set_next_event_phys(unsigned long evt,
 	return 0;
 }
 
+static u64 arch_counter_get_cnt_mem(struct arch_timer *t, int offset_lo)
+{
+	u32 cnt_lo, cnt_hi, tmp_hi;
+
+	do {
+		cnt_hi = readl_relaxed(t->base + offset_lo + 4);
+		cnt_lo = readl_relaxed(t->base + offset_lo);
+		tmp_hi = readl_relaxed(t->base + offset_lo + 4);
+	} while (cnt_hi != tmp_hi);
+
+	return ((u64) cnt_hi << 32) | cnt_lo;
+}
+
 static __always_inline void set_next_event_mem(const int access, unsigned long evt,
 					   struct clock_event_device *clk)
 {
+	struct arch_timer *timer = to_arch_timer(clk);
 	unsigned long ctrl;
+	u64 cnt;
+
 	ctrl = arch_timer_reg_read(access, ARCH_TIMER_REG_CTRL, clk);
 	ctrl |= ARCH_TIMER_CTRL_ENABLE;
 	ctrl &= ~ARCH_TIMER_CTRL_IT_MASK;
 
-	arch_timer_reg_write(access, ARCH_TIMER_REG_TVAL, evt, clk);
+	if (access ==  ARCH_TIMER_MEM_VIRT_ACCESS)
+		cnt = arch_counter_get_cnt_mem(timer, CNTVCT_LO);
+	else
+		cnt = arch_counter_get_cnt_mem(timer, CNTPCT_LO);
+
+	arch_timer_reg_write(access, ARCH_TIMER_REG_CVAL, evt + cnt, clk);
 	arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, clk);
 }
 
@@ -970,15 +1004,7 @@ bool arch_timer_evtstrm_available(void)
 
 static u64 arch_counter_get_cntvct_mem(void)
 {
-	u32 vct_lo, vct_hi, tmp_hi;
-
-	do {
-		vct_hi = readl_relaxed(arch_timer_mem->base + CNTVCT_HI);
-		vct_lo = readl_relaxed(arch_timer_mem->base + CNTVCT_LO);
-		tmp_hi = readl_relaxed(arch_timer_mem->base + CNTVCT_HI);
-	} while (vct_hi != tmp_hi);
-
-	return ((u64) vct_hi << 32) | vct_lo;
+	return arch_counter_get_cnt_mem(arch_timer_mem, CNTVCT_LO);
 }
 
 static struct arch_timer_kvm_info arch_timer_kvm_info;