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From:   Marc Zyngier <maz@kernel.org>
To:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Shier <pshier@google.com>,
        Raghavendra Rao Ananta <rananta@google.com>,
        Ricardo Koller <ricarkol@google.com>,
        Oliver Upton <oupton@google.com>,
        Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        kernel-team@android.com
Subject: [PATCH 03/13] clocksource/arm_arch_timer: Move system register timer programming over to CVAL
Date:   Mon,  9 Aug 2021 16:26:41 +0100
Message-Id: <20210809152651.2297337-4-maz@kernel.org>
In-Reply-To: <20210809152651.2297337-1-maz@kernel.org>
References: <20210809152651.2297337-1-maz@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

In order to cope better with high frequency counters, move the
programming of the timers from the countdown timer (TVAL) over
to the comparator (CVAL).

The programming model is slightly different, as we now need to
read the current counter value to have an absolute deadline
instead of a relative one.

There is a small overhead to this change, which we will address
in the following patches.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm/include/asm/arch_timer.h    | 14 ++++++++----
 arch/arm64/include/asm/arch_timer.h  | 16 +++++++++-----
 drivers/clocksource/arm_arch_timer.c | 32 +++++++++++++++++++++++++---
 include/clocksource/arm_arch_timer.h |  1 +
 4 files changed, 51 insertions(+), 12 deletions(-)

diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
index 88075c7f4bfd..b48de9d26f27 100644
--- a/arch/arm/include/asm/arch_timer.h
+++ b/arch/arm/include/asm/arch_timer.h
@@ -31,18 +31,22 @@ void arch_timer_reg_write_cp15(int access, enum arch_timer_reg reg, u64 val)
 		case ARCH_TIMER_REG_CTRL:
 			asm volatile("mcr p15, 0, %0, c14, c2, 1" : : "r" ((u32)val));
 			break;
-		case ARCH_TIMER_REG_TVAL:
-			asm volatile("mcr p15, 0, %0, c14, c2, 0" : : "r" ((u32)val));
+		case ARCH_TIMER_REG_CVAL:
+			asm volatile("mcrr p15, 2, %Q0, %R0, c14" : : "r" (val));
 			break;
+		case ARCH_TIMER_REG_TVAL:
+			BUG();
 		}
 	} else if (access == ARCH_TIMER_VIRT_ACCESS) {
 		switch (reg) {
 		case ARCH_TIMER_REG_CTRL:
 			asm volatile("mcr p15, 0, %0, c14, c3, 1" : : "r" ((u32)val));
 			break;
-		case ARCH_TIMER_REG_TVAL:
-			asm volatile("mcr p15, 0, %0, c14, c3, 0" : : "r" ((u32)val));
+		case ARCH_TIMER_REG_CVAL:
+			asm volatile("mcrr p15, 3, %Q0, %R0, c14" : : "r" (val));
 			break;
+		case ARCH_TIMER_REG_TVAL:
+			BUG();
 		}
 	}
 
@@ -60,6 +64,7 @@ u32 arch_timer_reg_read_cp15(int access, enum arch_timer_reg reg)
 			asm volatile("mrc p15, 0, %0, c14, c2, 1" : "=r" (val));
 			break;
 		case ARCH_TIMER_REG_TVAL:
+		case ARCH_TIMER_REG_CVAL:
 			BUG();
 		}
 	} else if (access == ARCH_TIMER_VIRT_ACCESS) {
@@ -68,6 +73,7 @@ u32 arch_timer_reg_read_cp15(int access, enum arch_timer_reg reg)
 			asm volatile("mrc p15, 0, %0, c14, c3, 1" : "=r" (val));
 			break;
 		case ARCH_TIMER_REG_TVAL:
+		case ARCH_TIMER_REG_CVAL:
 			BUG();
 		}
 	}
diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index 107afb721749..6ceb050ae7b9 100644
--- a/arch/arm64/include/asm/arch_timer.h
+++ b/arch/arm64/include/asm/arch_timer.h
@@ -96,18 +96,22 @@ void arch_timer_reg_write_cp15(int access, enum arch_timer_reg reg, u64 val)
 		case ARCH_TIMER_REG_CTRL:
 			write_sysreg(val, cntp_ctl_el0);
 			break;
-		case ARCH_TIMER_REG_TVAL:
-			write_sysreg(val, cntp_tval_el0);
+		case ARCH_TIMER_REG_CVAL:
+			write_sysreg(val, cntp_cval_el0);
 			break;
+		case ARCH_TIMER_REG_TVAL:
+			BUG();
 		}
 	} else if (access == ARCH_TIMER_VIRT_ACCESS) {
 		switch (reg) {
 		case ARCH_TIMER_REG_CTRL:
 			write_sysreg(val, cntv_ctl_el0);
 			break;
-		case ARCH_TIMER_REG_TVAL:
-			write_sysreg(val, cntv_tval_el0);
+		case ARCH_TIMER_REG_CVAL:
+			write_sysreg(val, cntv_cval_el0);
 			break;
+		case ARCH_TIMER_REG_TVAL:
+			BUG();
 		}
 	}
 
@@ -115,13 +119,14 @@ void arch_timer_reg_write_cp15(int access, enum arch_timer_reg reg, u64 val)
 }
 
 static __always_inline
-u32 arch_timer_reg_read_cp15(int access, enum arch_timer_reg reg)
+u64 arch_timer_reg_read_cp15(int access, enum arch_timer_reg reg)
 {
 	if (access == ARCH_TIMER_PHYS_ACCESS) {
 		switch (reg) {
 		case ARCH_TIMER_REG_CTRL:
 			return read_sysreg(cntp_ctl_el0);
 		case ARCH_TIMER_REG_TVAL:
+		case ARCH_TIMER_REG_CVAL:
 			break;
 		}
 	} else if (access == ARCH_TIMER_VIRT_ACCESS) {
@@ -129,6 +134,7 @@ u32 arch_timer_reg_read_cp15(int access, enum arch_timer_reg reg)
 		case ARCH_TIMER_REG_CTRL:
 			return read_sysreg(cntv_ctl_el0);
 		case ARCH_TIMER_REG_TVAL:
+		case ARCH_TIMER_REG_CVAL:
 			break;
 		}
 	}
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 0b2bac3ef7ce..898a07dc01cd 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -112,6 +112,8 @@ 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:
+			BUG();
 		}
 	} else if (access == ARCH_TIMER_MEM_VIRT_ACCESS) {
 		struct arch_timer *timer = to_arch_timer(clk);
@@ -122,6 +124,8 @@ 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:
+			BUG();
 		}
 	} else {
 		arch_timer_reg_write_cp15(access, reg, val);
@@ -141,6 +145,7 @@ u32 arch_timer_reg_read(int access, enum arch_timer_reg reg,
 			val = readl_relaxed(timer->base + CNTP_CTL);
 			break;
 		case ARCH_TIMER_REG_TVAL:
+		case ARCH_TIMER_REG_CVAL:
 			BUG();
 		}
 	} else if (access == ARCH_TIMER_MEM_VIRT_ACCESS) {
@@ -150,6 +155,7 @@ u32 arch_timer_reg_read(int access, enum arch_timer_reg reg,
 			val = readl_relaxed(timer->base + CNTV_CTL);
 			break;
 		case ARCH_TIMER_REG_TVAL:
+		case ARCH_TIMER_REG_CVAL:
 			BUG();
 		}
 	} else {
@@ -687,10 +693,18 @@ static __always_inline void set_next_event(const int access, unsigned long evt,
 					   struct clock_event_device *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_PHYS_ACCESS)
+		cnt = __arch_counter_get_cntpct();
+	else
+		cnt = __arch_counter_get_cntvct();
+
+	arch_timer_reg_write(access, ARCH_TIMER_REG_CVAL, evt + cnt, clk);
 	arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, clk);
 }
 
@@ -708,17 +722,29 @@ static int arch_timer_set_next_event_phys(unsigned long evt,
 	return 0;
 }
 
+static __always_inline void set_next_event_mem(const int access, unsigned long evt,
+					   struct clock_event_device *clk)
+{
+	unsigned long ctrl;
+	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);
+	arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, clk);
+}
+
 static int arch_timer_set_next_event_virt_mem(unsigned long evt,
 					      struct clock_event_device *clk)
 {
-	set_next_event(ARCH_TIMER_MEM_VIRT_ACCESS, evt, clk);
+	set_next_event_mem(ARCH_TIMER_MEM_VIRT_ACCESS, evt, clk);
 	return 0;
 }
 
 static int arch_timer_set_next_event_phys_mem(unsigned long evt,
 					      struct clock_event_device *clk)
 {
-	set_next_event(ARCH_TIMER_MEM_PHYS_ACCESS, evt, clk);
+	set_next_event_mem(ARCH_TIMER_MEM_PHYS_ACCESS, evt, clk);
 	return 0;
 }
 
diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h
index 73c7139c866f..d59537afb29d 100644
--- a/include/clocksource/arm_arch_timer.h
+++ b/include/clocksource/arm_arch_timer.h
@@ -25,6 +25,7 @@
 enum arch_timer_reg {
 	ARCH_TIMER_REG_CTRL,
 	ARCH_TIMER_REG_TVAL,
+	ARCH_TIMER_REG_CVAL,
 };
 
 enum arch_timer_ppi_nr {
-- 
2.30.2