[PATCH v4 0/6] Add module support for Arm64 Exynos MCT driver

[PATCH v4 0/6] Add module support for Arm64 Exynos MCT driver

[Will McVicker]

This series adds support to build the Arm64 Exynos MCT driver as a module.
This is only possible on Arm64 SoCs since they can use the Arm architected
timer as the clocksource. Once the Exynos MCT module is loaded and the
device probes, the MCT is used as the wakeup source for the arch_timer to
ensure the device can wakeup from the "c2" idle state.

These patches are originally from the downstream Pixel 6 (gs101) kernel
found at [1] and have been adapted for upstream. Not only has the Exynos MCT
driver been shipping as a module in the field with Android, but I've also
tested this series with the upstream kernel on my Pixel 6 Pro.

In addition, I verified that the Exynos MCT module cannot be unloaded on my
Pixel 6. This is due to /sys/module/exynos_mct/refcnt > 0. So if you try,
you'll get this:

  root@google-gs:~# rmmod exynos_mct
  rmmod: ERROR: Module exynos_mct is in use
  root@google-gs:~# cat /sys/module/exynos_mct/refcnt
  9

Thanks,
Will

Note1, instructions to build and flash a Pixel 6 device with the upstream
kernel can be found at [2].

Note2, this series is based off of krzk/for-next commit a15edf91668b ("Merge
branch 'next/dt64' into for-next") with [3] on top.

[1] https://android.googlesource.com/kernel/gs/+log/refs/heads/android-gs-raviole-5.10-android12-d1
[2] https://git.codelinaro.org/linaro/googlelt/pixelscripts/-/blob/clo/main/README.md?ref_type=heads
[3] https://lore.kernel.org/linux-arm-kernel/20250602151853.1942521-1-daniel.lezcano@linaro.org/

Cc: Alim Akhtar <alim.akhtar@samsung.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Donghoon Yu <hoony.yu@samsung.com>
Cc: Hosung Kim <hosung0.kim@samsung.com>
Cc: kernel-team@android.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: Rob Herring <robh@kernel.org>
Cc: Saravana Kannan <saravanak@google.com>
Cc: John Stultz <jstultz@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Youngmin Nam <youngmin.nam@samsung.com>
Cc: Peter Griffin <peter.griffin@linaro.org>
Cc: Tudor Ambarus <tudor.ambarus@linaro.org>
Cc: André Draszik <andre.draszik@linaro.org>
Cc: Will Deacon <will@kernel.org>
Cc: Conor Dooley <conor+dt@kernel.org>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: linux-samsung-soc@vger.kernel.org

---
Changes in v4:
- Missed the "v3" string in the previous series for the actual patches
- Re-generated patches with --base a15edf91668beefdb5171c53fa698c9b43dd1e0d
  for kernel test robot.

Changes in v3:
- Rebased on top of Daniel's timer modularization prep series [3] and
  krzk/for-next commit a15edf91668b ("Merge branch 'next/dt64' into
  for-next")
- Added owner references to Exynos MCT clocksource and clockevent objects.
- Dropped #ifdef MODULE conditional section in favor of just using
  module_platform_driver() which will properly handle setting up the
  of_device_id table based on if the driver is built-in or a module.
- Update commit message for patch 2 based on John's feedback.
- Dropped DT change from v2 as it was picked up by Krzysztof for CPU Idle.

Changes in v2:
- Re-worked patch v1 5 based on Rob Herring's review to use the compatible
  data for retrieving the mct_init function pointer.
- Updated the Kconfig logic to disallow building the Exynos MCT driver as
  a module for ARM32 configurations based on Krzysztof Kozlowski's findings.
- Added comments and clarified commit messages in patches 1 and 2 based on
  reviews from John Stultz and Youngmin Nam.
- Fixed an issue found during testing that resulted in the device getting
  stuck on boot. This is included in v2 as patch 5.
- Collected *-by tags
- Rebased to the latest linux-next/master.
---
 

Donghoon Yu (1):
  clocksource/drivers/exynos_mct: Add module support

Hosung Kim (1):
  clocksource/drivers/exynos_mct: Set local timer interrupts as percpu

Will McVicker (4):
  of/irq: Export of_irq_count for modules
  clocksource/drivers/exynos_mct: Don't register as a sched_clock on
    arm64
  clocksource/drivers/exynos_mct: Fix uninitialized irq name warning
  arm64: exynos: Drop select CLKSRC_EXYNOS_MCT

 arch/arm64/Kconfig.platforms     |  1 -
 drivers/clocksource/Kconfig      |  3 +-
 drivers/clocksource/exynos_mct.c | 75 ++++++++++++++++++++++++++------
 drivers/of/irq.c                 |  1 +
 4 files changed, 64 insertions(+), 16 deletions(-)


base-commit: a15edf91668beefdb5171c53fa698c9b43dd1e0d
prerequisite-patch-id: 0c5b7e9fb27295e0c125c537ac80d1eb16cef60d
prerequisite-patch-id: 6a9b683baee83ddc2b2fada31479b27b53469759
prerequisite-patch-id: b9cbd59ff2f4c905001ecb02868d20fb004034cc
prerequisite-patch-id: cdde1a76624089aa818cb35e612f880107bdc073
prerequisite-patch-id: cec67e07038c7aa93a2b53879781626d738cd199
prerequisite-patch-id: 8fda377fcaf407026f04f2a547086cf1ecf4efc9
prerequisite-patch-id: dce925ac224bb361c74fdb23126fab53e7c5c26b
-- 
2.50.0.rc2.761.g2dc52ea45b-goog

[PATCH v4 1/6] of/irq: Export of_irq_count for modules

[Will McVicker]

Need to export `of_irq_count` in preparation for modularizing the Exynos
MCT driver which uses this API for setting up the timer IRQs.

Acked-by: Rob Herring (Arm) <robh@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Reviewed-by: Youngmin Nam <youngmin.nam@samsung.com>
Tested-by: Youngmin Nam <youngmin.nam@samsung.com>
Signed-off-by: Will McVicker <willmcvicker@google.com>
---
 drivers/of/irq.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/of/irq.c b/drivers/of/irq.c
index f8ad79b9b1c9..5adda1dac3cf 100644
--- a/drivers/of/irq.c
+++ b/drivers/of/irq.c
@@ -519,6 +519,7 @@ int of_irq_count(struct device_node *dev)
 
 	return nr;
 }
+EXPORT_SYMBOL_GPL(of_irq_count);
 
 /**
  * of_irq_to_resource_table - Fill in resource table with node's IRQ info
-- 
2.50.0.rc2.761.g2dc52ea45b-goog

[PATCH v4 2/6] clocksource/drivers/exynos_mct: Don't register as a sched_clock on arm64

[Will McVicker]

The MCT register is unfortunately very slow to access, but importantly
does not halt in the c2 idle state. So for ARM64, we can improve
performance by not registering the MCT for sched_clock, allowing the
system to use the faster ARM architected timer for sched_clock instead.

The MCT is still registered as a clocksource, and a clockevent in order
to be a wakeup source for the arch_timer to exit the "c2" idle state.

Since ARM32 SoCs don't have an architected timer, the MCT must continue
to be used for sched_clock. Detailed discussion on this topic can be
found at [1].

[1] https://lore.kernel.org/linux-samsung-soc/1400188079-21832-1-git-send-email-chirantan@chromium.org/

[Original commit from https://android.googlesource.com/kernel/gs/+/630817f7080e92c5e0216095ff52f6eb8dd00727

Signed-off-by: Donghoon Yu <hoony.yu@samsung.com>
Signed-off-by: Youngmin Nam <youngmin.nam@samsung.com>
Reviewed-by: Youngmin Nam <youngmin.nam@samsung.com>
Acked-by: John Stultz <jstultz@google.com>
Tested-by: Youngmin Nam <youngmin.nam@samsung.com>
Signed-off-by: Will McVicker <willmcvicker@google.com>
---
 drivers/clocksource/exynos_mct.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
index da09f467a6bb..96361d5dc57d 100644
--- a/drivers/clocksource/exynos_mct.c
+++ b/drivers/clocksource/exynos_mct.c
@@ -219,12 +219,18 @@ static struct clocksource mct_frc = {
 	.resume		= exynos4_frc_resume,
 };
 
+/*
+ * Since ARM devices do not have an architected timer, they need to continue
+ * using the MCT as the main clocksource for timekeeping, sched_clock, and the
+ * delay timer. For AARCH64 SoCs, the architected timer is the preferred
+ * clocksource due to it's superior performance.
+ */
+#if defined(CONFIG_ARM)
 static u64 notrace exynos4_read_sched_clock(void)
 {
 	return exynos4_read_count_32();
 }
 
-#if defined(CONFIG_ARM)
 static struct delay_timer exynos4_delay_timer;
 
 static cycles_t exynos4_read_current_timer(void)
@@ -250,12 +256,13 @@ static int __init exynos4_clocksource_init(bool frc_shared)
 	exynos4_delay_timer.read_current_timer = &exynos4_read_current_timer;
 	exynos4_delay_timer.freq = clk_rate;
 	register_current_timer_delay(&exynos4_delay_timer);
+
+	sched_clock_register(exynos4_read_sched_clock, 32, clk_rate);
 #endif
 
 	if (clocksource_register_hz(&mct_frc, clk_rate))
 		panic("%s: can't register clocksource\n", mct_frc.name);
 
-	sched_clock_register(exynos4_read_sched_clock, 32, clk_rate);
 
 	return 0;
 }
-- 
2.50.0.rc2.761.g2dc52ea45b-goog

[PATCH v4 3/6] clocksource/drivers/exynos_mct: Set local timer interrupts as percpu

[Will McVicker]

From: Hosung Kim <hosung0.kim@samsung.com>

To allow the CPU to handle it's own clock events, we need to set the
IRQF_PERCPU flag. This prevents the local timer interrupts from
migrating to other CPUs.

Signed-off-by: Hosung Kim <hosung0.kim@samsung.com>
[Original commit from https://android.googlesource.com/kernel/gs/+/03267fad19f093bac979ca78309483e9eb3a8d16]
Reviewed-by: Peter Griffin <peter.griffin@linaro.org>
Reviewed-by: Youngmin Nam <youngmin.nam@samsung.com>
Tested-by: Youngmin Nam <youngmin.nam@samsung.com>
Signed-off-by: Will McVicker <willmcvicker@google.com>
---
 drivers/clocksource/exynos_mct.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
index 96361d5dc57d..a5ef7d64b1c2 100644
--- a/drivers/clocksource/exynos_mct.c
+++ b/drivers/clocksource/exynos_mct.c
@@ -596,7 +596,8 @@ static int __init exynos4_timer_interrupts(struct device_node *np,
 			irq_set_status_flags(mct_irq, IRQ_NOAUTOEN);
 			if (request_irq(mct_irq,
 					exynos4_mct_tick_isr,
-					IRQF_TIMER | IRQF_NOBALANCING,
+					IRQF_TIMER | IRQF_NOBALANCING |
+					IRQF_PERCPU,
 					pcpu_mevt->name, pcpu_mevt)) {
 				pr_err("exynos-mct: cannot register IRQ (cpu%d)\n",
 									cpu);
-- 
2.50.0.rc2.761.g2dc52ea45b-goog

[PATCH v4 4/6] clocksource/drivers/exynos_mct: Fix uninitialized irq name warning

[Will McVicker]

The Exynos MCT driver doesn't set the clocksource name until the CPU
hotplug state is setup which happens after the IRQs are requested. This
results in an empty IRQ name which leads to the below warning at
proc_create() time. When this happens, the userdata partition fails to
mount and the device gets stuck in an endless loop printing the error:

  root '/dev/disk/by-partlabel/userdata' doesn't exist or does not contain a /dev.

To fix this, we just need to initialize the name before requesting the
IRQs.

Warning from Pixel 6 kernel log:

[  T430] name len 0
[  T430] WARNING: CPU: 6 PID: 430 at fs/proc/generic.c:407 __proc_create+0x258/0x2b4
[  T430] Modules linked in: dwc3_exynos(E+)
[  T430]  ufs_exynos(E+) phy_exynos_ufs(E)
[  T430]  phy_exynos5_usbdrd(E) exynos_usi(E+) exynos_mct(E+) s3c2410_wdt(E)
[  T430]  arm_dsu_pmu(E) simplefb(E)
[  T430] CPU: 6 UID: 0 PID: 430 Comm: (udev-worker) Tainted:
         ... 6.14.0-next-20250331-4k-00008-g59adf909e40e #1 ...
[  T430] Tainted: [W]=WARN, [E]=UNSIGNED_MODULE
[  T430] Hardware name: Raven (DT)
[...]
[  T430] Call trace:
[  T430]  __proc_create+0x258/0x2b4 (P)
[  T430]  proc_mkdir+0x40/0xa0
[  T430]  register_handler_proc+0x118/0x140
[  T430]  __setup_irq+0x460/0x6d0
[  T430]  request_threaded_irq+0xcc/0x1b0
[  T430]  mct_init_dt+0x244/0x604 [exynos_mct ...]
[  T430]  mct_init_spi+0x18/0x34 [exynos_mct ...]
[  T430]  exynos4_mct_probe+0x30/0x4c [exynos_mct ...]
[  T430]  platform_probe+0x6c/0xe4
[  T430]  really_probe+0xf4/0x38c
[...]
[  T430]  driver_register+0x6c/0x140
[  T430]  __platform_driver_register+0x28/0x38
[  T430]  exynos4_mct_driver_init+0x24/0xfe8 [exynos_mct ...]
[  T430]  do_one_initcall+0x84/0x3c0
[  T430]  do_init_module+0x58/0x208
[  T430]  load_module+0x1de0/0x2500
[  T430]  init_module_from_file+0x8c/0xdc

Reviewed-by: Peter Griffin <peter.griffin@linaro.org>
Reviewed-by: Youngmin Nam <youngmin.nam@samsung.com>
Tested-by: Youngmin Nam <youngmin.nam@samsung.com>
Signed-off-by: Will McVicker <willmcvicker@google.com>
---
 drivers/clocksource/exynos_mct.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
index a5ef7d64b1c2..62febeb4e1de 100644
--- a/drivers/clocksource/exynos_mct.c
+++ b/drivers/clocksource/exynos_mct.c
@@ -465,8 +465,6 @@ static int exynos4_mct_starting_cpu(unsigned int cpu)
 		per_cpu_ptr(&percpu_mct_tick, cpu);
 	struct clock_event_device *evt = &mevt->evt;
 
-	snprintf(mevt->name, sizeof(mevt->name), "mct_tick%d", cpu);
-
 	evt->name = mevt->name;
 	evt->cpumask = cpumask_of(cpu);
 	evt->set_next_event = exynos4_tick_set_next_event;
@@ -567,6 +565,14 @@ static int __init exynos4_timer_interrupts(struct device_node *np,
 	for (i = MCT_L0_IRQ; i < nr_irqs; i++)
 		mct_irqs[i] = irq_of_parse_and_map(np, i);
 
+	for_each_possible_cpu(cpu) {
+		struct mct_clock_event_device *mevt =
+		    per_cpu_ptr(&percpu_mct_tick, cpu);
+
+		snprintf(mevt->name, sizeof(mevt->name), "mct_tick%d",
+			 cpu);
+	}
+
 	if (mct_int_type == MCT_INT_PPI) {
 
 		err = request_percpu_irq(mct_irqs[MCT_L0_IRQ],
-- 
2.50.0.rc2.761.g2dc52ea45b-goog

[PATCH v4 5/6] clocksource/drivers/exynos_mct: Add module support

[Will McVicker]

From: Donghoon Yu <hoony.yu@samsung.com>

On Arm64 platforms the Exynos MCT driver can be built as a module. On
boot (and even after boot) the arch_timer is used as the clocksource and
tick timer. Once the MCT driver is loaded, it can be used as the wakeup
source for the arch_timer.

Signed-off-by: Donghoon Yu <hoony.yu@samsung.com>
Signed-off-by: Youngmin Nam <youngmin.nam@samsung.com>
[original commit from https://android.googlesource.com/kernel/gs/+/8a52a8288ec7d88ff78f0b37480dbb0e9c65bbfd]
Reviewed-by: Youngmin Nam <youngmin.nam@samsung.com>
Tested-by: Youngmin Nam <youngmin.nam@samsung.com>
Signed-off-by: Will McVicker <willmcvicker@google.com>
---
 drivers/clocksource/Kconfig      |  3 +-
 drivers/clocksource/exynos_mct.c | 51 ++++++++++++++++++++++++++------
 2 files changed, 44 insertions(+), 10 deletions(-)

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 645f517a1ac2..d657c8ddc96b 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -451,7 +451,8 @@ config ATMEL_TCB_CLKSRC
 	  Support for Timer Counter Blocks on Atmel SoCs.
 
 config CLKSRC_EXYNOS_MCT
-	bool "Exynos multi core timer driver" if COMPILE_TEST
+	tristate "Exynos multi core timer driver" if ARM64
+	default y if ARCH_EXYNOS || COMPILE_TEST
 	depends on ARM || ARM64
 	depends on ARCH_ARTPEC || ARCH_EXYNOS || COMPILE_TEST
 	help
diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
index 62febeb4e1de..5075ebe052a7 100644
--- a/drivers/clocksource/exynos_mct.c
+++ b/drivers/clocksource/exynos_mct.c
@@ -15,9 +15,11 @@
 #include <linux/cpu.h>
 #include <linux/delay.h>
 #include <linux/percpu.h>
+#include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_irq.h>
 #include <linux/of_address.h>
+#include <linux/platform_device.h>
 #include <linux/clocksource.h>
 #include <linux/sched_clock.h>
 
@@ -217,6 +219,7 @@ static struct clocksource mct_frc = {
 	.mask		= CLOCKSOURCE_MASK(32),
 	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
 	.resume		= exynos4_frc_resume,
+	.owner		= THIS_MODULE,
 };
 
 /*
@@ -241,7 +244,7 @@ static cycles_t exynos4_read_current_timer(void)
 }
 #endif
 
-static int __init exynos4_clocksource_init(bool frc_shared)
+static int exynos4_clocksource_init(bool frc_shared)
 {
 	/*
 	 * When the frc is shared, the main processor should have already
@@ -336,6 +339,7 @@ static struct clock_event_device mct_comp_device = {
 	.set_state_oneshot	= mct_set_state_shutdown,
 	.set_state_oneshot_stopped = mct_set_state_shutdown,
 	.tick_resume		= mct_set_state_shutdown,
+	.owner			= THIS_MODULE,
 };
 
 static irqreturn_t exynos4_mct_comp_isr(int irq, void *dev_id)
@@ -476,6 +480,7 @@ static int exynos4_mct_starting_cpu(unsigned int cpu)
 	evt->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT |
 			CLOCK_EVT_FEAT_PERCPU;
 	evt->rating = MCT_CLKEVENTS_RATING;
+	evt->owner = THIS_MODULE;
 
 	exynos4_mct_write(TICK_BASE_CNT, mevt->base + MCT_L_TCNTB_OFFSET);
 
@@ -511,7 +516,7 @@ static int exynos4_mct_dying_cpu(unsigned int cpu)
 	return 0;
 }
 
-static int __init exynos4_timer_resources(struct device_node *np)
+static int exynos4_timer_resources(struct device_node *np)
 {
 	struct clk *mct_clk, *tick_clk;
 
@@ -539,7 +544,7 @@ static int __init exynos4_timer_resources(struct device_node *np)
  * @local_idx: array mapping CPU numbers to local timer indices
  * @nr_local: size of @local_idx array
  */
-static int __init exynos4_timer_interrupts(struct device_node *np,
+static int exynos4_timer_interrupts(struct device_node *np,
 					   unsigned int int_type,
 					   const u32 *local_idx,
 					   size_t nr_local)
@@ -652,7 +657,7 @@ static int __init exynos4_timer_interrupts(struct device_node *np,
 	return err;
 }
 
-static int __init mct_init_dt(struct device_node *np, unsigned int int_type)
+static int mct_init_dt(struct device_node *np, unsigned int int_type)
 {
 	bool frc_shared = of_property_read_bool(np, "samsung,frc-shared");
 	u32 local_idx[MCT_NR_LOCAL] = {0};
@@ -700,15 +705,43 @@ static int __init mct_init_dt(struct device_node *np, unsigned int int_type)
 	return exynos4_clockevent_init();
 }
 
-
-static int __init mct_init_spi(struct device_node *np)
+static int mct_init_spi(struct device_node *np)
 {
 	return mct_init_dt(np, MCT_INT_SPI);
 }
 
-static int __init mct_init_ppi(struct device_node *np)
+static int mct_init_ppi(struct device_node *np)
 {
 	return mct_init_dt(np, MCT_INT_PPI);
 }
-TIMER_OF_DECLARE(exynos4210, "samsung,exynos4210-mct", mct_init_spi);
-TIMER_OF_DECLARE(exynos4412, "samsung,exynos4412-mct", mct_init_ppi);
+
+static int exynos4_mct_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	int (*mct_init)(struct device_node *np);
+
+	mct_init = of_device_get_match_data(dev);
+	if (!mct_init)
+		return -EINVAL;
+
+	return mct_init(dev->of_node);
+}
+
+static const struct of_device_id exynos4_mct_match_table[] = {
+	{ .compatible = "samsung,exynos4210-mct", .data = &mct_init_spi, },
+	{ .compatible = "samsung,exynos4412-mct", .data = &mct_init_ppi, },
+	{}
+};
+MODULE_DEVICE_TABLE(of, exynos4_mct_match_table);
+
+static struct platform_driver exynos4_mct_driver = {
+	.probe		= exynos4_mct_probe,
+	.driver		= {
+		.name	= "exynos-mct",
+		.of_match_table = exynos4_mct_match_table,
+	},
+};
+module_platform_driver(exynos4_mct_driver);
+
+MODULE_DESCRIPTION("Exynos Multi Core Timer Driver");
+MODULE_LICENSE("GPL");
-- 
2.50.0.rc2.761.g2dc52ea45b-goog

[PATCH v4 6/6] arm64: exynos: Drop select CLKSRC_EXYNOS_MCT

[Will McVicker]

Since the Exynos MCT driver can be built as a module for some Arm64 SoCs
like gs101, drop force-selecting it as a built-in driver by ARCH_EXYNOS
and instead depend on `default y if ARCH_EXYNOS` to select it
automatically. This allows platforms like Android to build the driver as
a module if desired.

Reviewed-by: Youngmin Nam <youngmin.nam@samsung.com>
Tested-by: Youngmin Nam <youngmin.nam@samsung.com>
Signed-off-by: Will McVicker <willmcvicker@google.com>
---
 arch/arm64/Kconfig.platforms | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/arm64/Kconfig.platforms b/arch/arm64/Kconfig.platforms
index a541bb029aa4..46825b02d099 100644
--- a/arch/arm64/Kconfig.platforms
+++ b/arch/arm64/Kconfig.platforms
@@ -109,7 +109,6 @@ config ARCH_BLAIZE
 config ARCH_EXYNOS
 	bool "Samsung Exynos SoC family"
 	select COMMON_CLK_SAMSUNG
-	select CLKSRC_EXYNOS_MCT
 	select EXYNOS_PM_DOMAINS if PM_GENERIC_DOMAINS
 	select EXYNOS_PMU
 	select PINCTRL
-- 
2.50.0.rc2.761.g2dc52ea45b-goog

Re: [PATCH v4 5/6] clocksource/drivers/exynos_mct: Add module support

[Daniel Lezcano]

On Fri, Jun 20, 2025 at 11:17:08AM -0700, Will McVicker wrote:
> From: Donghoon Yu <hoony.yu@samsung.com>
> 
> On Arm64 platforms the Exynos MCT driver can be built as a module. On
> boot (and even after boot) the arch_timer is used as the clocksource and
> tick timer. Once the MCT driver is loaded, it can be used as the wakeup
> source for the arch_timer.
> 
> Signed-off-by: Donghoon Yu <hoony.yu@samsung.com>
> Signed-off-by: Youngmin Nam <youngmin.nam@samsung.com>
> [original commit from https://android.googlesource.com/kernel/gs/+/8a52a8288ec7d88ff78f0b37480dbb0e9c65bbfd]
> Reviewed-by: Youngmin Nam <youngmin.nam@samsung.com>
> Tested-by: Youngmin Nam <youngmin.nam@samsung.com>
> Signed-off-by: Will McVicker <willmcvicker@google.com>
> ---

...

> -static int __init mct_init_spi(struct device_node *np)

__init_or_module

> +static int mct_init_spi(struct device_node *np)
>  {
>  	return mct_init_dt(np, MCT_INT_SPI);
>  }
>  
> -static int __init mct_init_ppi(struct device_node *np)
> +static int mct_init_ppi(struct device_node *np)
>  {
>  	return mct_init_dt(np, MCT_INT_PPI);
>  }
> -TIMER_OF_DECLARE(exynos4210, "samsung,exynos4210-mct", mct_init_spi);
> -TIMER_OF_DECLARE(exynos4412, "samsung,exynos4412-mct", mct_init_ppi);

Are you sure this is not going to hurt the ARM platforms ? Here the
timer is enabled very early in the boot process while with this change
the timer will be available later.

> +static int exynos4_mct_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	int (*mct_init)(struct device_node *np);
> +
> +	mct_init = of_device_get_match_data(dev);
> +	if (!mct_init)
> +		return -EINVAL;
> +
> +	return mct_init(dev->of_node);
> +}
> +
> +static const struct of_device_id exynos4_mct_match_table[] = {
> +	{ .compatible = "samsung,exynos4210-mct", .data = &mct_init_spi, },
> +	{ .compatible = "samsung,exynos4412-mct", .data = &mct_init_ppi, },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, exynos4_mct_match_table);
> +
> +static struct platform_driver exynos4_mct_driver = {
> +	.probe		= exynos4_mct_probe,
> +	.driver		= {
> +		.name	= "exynos-mct",
> +		.of_match_table = exynos4_mct_match_table,
> +	},
> +};
> +module_platform_driver(exynos4_mct_driver);
> +
> +MODULE_DESCRIPTION("Exynos Multi Core Timer Driver");
> +MODULE_LICENSE("GPL");
> -- 
> 2.50.0.rc2.761.g2dc52ea45b-goog
> 

-- 

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Re: [PATCH v4 5/6] clocksource/drivers/exynos_mct: Add module support

[William McVicker]

On 06/24/2025, Daniel Lezcano wrote:
> On Fri, Jun 20, 2025 at 11:17:08AM -0700, Will McVicker wrote:
> > From: Donghoon Yu <hoony.yu@samsung.com>
> > 
> > On Arm64 platforms the Exynos MCT driver can be built as a module. On
> > boot (and even after boot) the arch_timer is used as the clocksource and
> > tick timer. Once the MCT driver is loaded, it can be used as the wakeup
> > source for the arch_timer.
> > 
> > Signed-off-by: Donghoon Yu <hoony.yu@samsung.com>
> > Signed-off-by: Youngmin Nam <youngmin.nam@samsung.com>
> > [original commit from https://android.googlesource.com/kernel/gs/+/8a52a8288ec7d88ff78f0b37480dbb0e9c65bbfd]
> > Reviewed-by: Youngmin Nam <youngmin.nam@samsung.com>
> > Tested-by: Youngmin Nam <youngmin.nam@samsung.com>
> > Signed-off-by: Will McVicker <willmcvicker@google.com>
> > ---
> 
> ...
> 
> > -static int __init mct_init_spi(struct device_node *np)
> 
> __init_or_module

Thanks, I'll update in v5.

> 
> > +static int mct_init_spi(struct device_node *np)
> >  {
> >  	return mct_init_dt(np, MCT_INT_SPI);
> >  }
> >  
> > -static int __init mct_init_ppi(struct device_node *np)
> > +static int mct_init_ppi(struct device_node *np)
> >  {
> >  	return mct_init_dt(np, MCT_INT_PPI);
> >  }
> > -TIMER_OF_DECLARE(exynos4210, "samsung,exynos4210-mct", mct_init_spi);
> > -TIMER_OF_DECLARE(exynos4412, "samsung,exynos4412-mct", mct_init_ppi);
> 
> Are you sure this is not going to hurt the ARM platforms ? Here the
> timer is enabled very early in the boot process while with this change
> the timer will be available later.

I took a second look at the TIMER_OF_DECLARE() macro and FWICT the timer will
only be enabled "very early" via timer_probe() if "MODULE" is not defined which
is only defined when this specific driver is compiled as a module. Note, this
"MODULE" define is not the same as the Kconfig option "CONFIG_MODULES".
That is why in my v1 and v2 patch [1] I had:

 #ifdef MODULE
   ...
   module_platform_driver(exynos4_mct_driver);
 #else
   TIMER_OF_DECLARE(...)
   TIMER_OF_DECLARE(...)
 #endif

However, I dropped that since Saravana mentioned that we should not be using
TIMER_OF_DECLARE() for drivers that can be modules. I don't have an ARM Exynos
device to verify dropping TIMER_OF_DECLARE() is safe. So if you and Saravana
agree, I can work on creating a patch to define TIMER_OF_DECLARE_MODULE() like
you proposed in [2] to handle this for all the drivers that are used for both ARM and
ARM64 SoCs.

Thanks,
Will

[1] https://lore.kernel.org/all/6e6b0f5f-ac60-48bb-af6c-fa58658d2639@linaro.org/
[2] https://lore.kernel.org/all/f2f914aa-c554-4135-afaa-f075537ed929@linaro.org/

<snip>

Re: [PATCH v4 5/6] clocksource/drivers/exynos_mct: Add module support

[Daniel Lezcano]

Hi Will,

sorry I missed to add you in Cc but the following proposal help in the 
module conversion:

https://lore.kernel.org/all/20250625085715.889837-1-daniel.lezcano@linaro.org/


On 25/06/2025 01:47, William McVicker wrote:
> On 06/24/2025, Daniel Lezcano wrote:
>> On Fri, Jun 20, 2025 at 11:17:08AM -0700, Will McVicker wrote:
>>> From: Donghoon Yu <hoony.yu@samsung.com>
>>>
>>> On Arm64 platforms the Exynos MCT driver can be built as a module. On
>>> boot (and even after boot) the arch_timer is used as the clocksource and
>>> tick timer. Once the MCT driver is loaded, it can be used as the wakeup
>>> source for the arch_timer.
>>>
>>> Signed-off-by: Donghoon Yu <hoony.yu@samsung.com>
>>> Signed-off-by: Youngmin Nam <youngmin.nam@samsung.com>
>>> [original commit from https://android.googlesource.com/kernel/gs/+/8a52a8288ec7d88ff78f0b37480dbb0e9c65bbfd]
>>> Reviewed-by: Youngmin Nam <youngmin.nam@samsung.com>
>>> Tested-by: Youngmin Nam <youngmin.nam@samsung.com>
>>> Signed-off-by: Will McVicker <willmcvicker@google.com>
>>> ---
>>
>> ...
>>
>>> -static int __init mct_init_spi(struct device_node *np)
>>
>> __init_or_module
> 
> Thanks, I'll update in v5.
> 
>>
>>> +static int mct_init_spi(struct device_node *np)
>>>   {
>>>   	return mct_init_dt(np, MCT_INT_SPI);
>>>   }
>>>   
>>> -static int __init mct_init_ppi(struct device_node *np)
>>> +static int mct_init_ppi(struct device_node *np)
>>>   {
>>>   	return mct_init_dt(np, MCT_INT_PPI);
>>>   }
>>> -TIMER_OF_DECLARE(exynos4210, "samsung,exynos4210-mct", mct_init_spi);
>>> -TIMER_OF_DECLARE(exynos4412, "samsung,exynos4412-mct", mct_init_ppi);
>>
>> Are you sure this is not going to hurt the ARM platforms ? Here the
>> timer is enabled very early in the boot process while with this change
>> the timer will be available later.
> 
> I took a second look at the TIMER_OF_DECLARE() macro and FWICT the timer will
> only be enabled "very early" via timer_probe() if "MODULE" is not defined which
> is only defined when this specific driver is compiled as a module. Note, this
> "MODULE" define is not the same as the Kconfig option "CONFIG_MODULES".
> That is why in my v1 and v2 patch [1] I had:
> 
>   #ifdef MODULE
>     ...
>     module_platform_driver(exynos4_mct_driver);
>   #else
>     TIMER_OF_DECLARE(...)
>     TIMER_OF_DECLARE(...)
>   #endif
> 
> However, I dropped that since Saravana mentioned that we should not be using
> TIMER_OF_DECLARE() for drivers that can be modules. I don't have an ARM Exynos
> device to verify dropping TIMER_OF_DECLARE() is safe. So if you and Saravana
> agree, I can work on creating a patch to define TIMER_OF_DECLARE_MODULE() like
> you proposed in [2] to handle this for all the drivers that are used for both ARM and
> ARM64 SoCs.
> 
> Thanks,
> Will
> 
> [1] https://lore.kernel.org/all/6e6b0f5f-ac60-48bb-af6c-fa58658d2639@linaro.org/
> [2] https://lore.kernel.org/all/f2f914aa-c554-4135-afaa-f075537ed929@linaro.org/
> 
> <snip>


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Re: [PATCH v4 0/6] Add module support for Arm64 Exynos MCT driver

[Daniel Lezcano]

On Fri, Jun 20, 2025 at 11:17:03AM -0700, Will McVicker wrote:
> This series adds support to build the Arm64 Exynos MCT driver as a module.
> This is only possible on Arm64 SoCs since they can use the Arm architected
> timer as the clocksource. Once the Exynos MCT module is loaded and the
> device probes, the MCT is used as the wakeup source for the arch_timer to
> ensure the device can wakeup from the "c2" idle state.
> 
> These patches are originally from the downstream Pixel 6 (gs101) kernel
> found at [1] and have been adapted for upstream. Not only has the Exynos MCT
> driver been shipping as a module in the field with Android, but I've also
> tested this series with the upstream kernel on my Pixel 6 Pro.
> 
> In addition, I verified that the Exynos MCT module cannot be unloaded on my
> Pixel 6. This is due to /sys/module/exynos_mct/refcnt > 0. So if you try,
> you'll get this:
> 
>   root@google-gs:~# rmmod exynos_mct
>   rmmod: ERROR: Module exynos_mct is in use
>   root@google-gs:~# cat /sys/module/exynos_mct/refcnt
>   9
> 
> Thanks,
> Will
> 
> Note1, instructions to build and flash a Pixel 6 device with the upstream
> kernel can be found at [2].
> 
> Note2, this series is based off of krzk/for-next commit a15edf91668b ("Merge
> branch 'next/dt64' into for-next") with [3] on top.
> 
> [1] https://android.googlesource.com/kernel/gs/+log/refs/heads/android-gs-raviole-5.10-android12-d1
> [2] https://git.codelinaro.org/linaro/googlelt/pixelscripts/-/blob/clo/main/README.md?ref_type=heads
> [3] https://lore.kernel.org/linux-arm-kernel/20250602151853.1942521-1-daniel.lezcano@linaro.org/
> 
> Cc: Alim Akhtar <alim.akhtar@samsung.com>
> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
> Cc: Donghoon Yu <hoony.yu@samsung.com>
> Cc: Hosung Kim <hosung0.kim@samsung.com>
> Cc: kernel-team@android.com
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Cc: Rob Herring <robh@kernel.org>
> Cc: Saravana Kannan <saravanak@google.com>
> Cc: John Stultz <jstultz@google.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Youngmin Nam <youngmin.nam@samsung.com>
> Cc: Peter Griffin <peter.griffin@linaro.org>
> Cc: Tudor Ambarus <tudor.ambarus@linaro.org>
> Cc: André Draszik <andre.draszik@linaro.org>
> Cc: Will Deacon <will@kernel.org>
> Cc: Conor Dooley <conor+dt@kernel.org>
> Cc: Krzysztof Kozlowski <krzk@kernel.org>
> Cc: linux-samsung-soc@vger.kernel.org
> 
> ---
> Changes in v4:
> - Missed the "v3" string in the previous series for the actual patches
> - Re-generated patches with --base a15edf91668beefdb5171c53fa698c9b43dd1e0d
>   for kernel test robot.
> 
> Changes in v3:
> - Rebased on top of Daniel's timer modularization prep series [3] and
>   krzk/for-next commit a15edf91668b ("Merge branch 'next/dt64' into
>   for-next")
> - Added owner references to Exynos MCT clocksource and clockevent objects.
> - Dropped #ifdef MODULE conditional section in favor of just using
>   module_platform_driver() which will properly handle setting up the
>   of_device_id table based on if the driver is built-in or a module.
> - Update commit message for patch 2 based on John's feedback.
> - Dropped DT change from v2 as it was picked up by Krzysztof for CPU Idle.
> 
> Changes in v2:
> - Re-worked patch v1 5 based on Rob Herring's review to use the compatible
>   data for retrieving the mct_init function pointer.
> - Updated the Kconfig logic to disallow building the Exynos MCT driver as
>   a module for ARM32 configurations based on Krzysztof Kozlowski's findings.
> - Added comments and clarified commit messages in patches 1 and 2 based on
>   reviews from John Stultz and Youngmin Nam.
> - Fixed an issue found during testing that resulted in the device getting
>   stuck on boot. This is included in v2 as patch 5.
> - Collected *-by tags
> - Rebased to the latest linux-next/master.
> ---

Applied, thanks

  -- Daniel

-- 

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Re: [PATCH v4 5/6] clocksource/drivers/exynos_mct: Add module support

[Daniel Lezcano]

Hi Will,


On 20/06/2025 20:17, Will McVicker wrote:

[ ... ]

> -TIMER_OF_DECLARE(exynos4210, "samsung,exynos4210-mct", mct_init_spi);
> -TIMER_OF_DECLARE(exynos4412, "samsung,exynos4412-mct", mct_init_ppi);

Was these changes tested on the ARM32 Exynos platforms ? Especially did 
you check if there is no boot time regression ?

> +static int exynos4_mct_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	int (*mct_init)(struct device_node *np);
> +
> +	mct_init = of_device_get_match_data(dev);
> +	if (!mct_init)
> +		return -EINVAL;
> +
> +	return mct_init(dev->of_node);
> +}
> +
> +static const struct of_device_id exynos4_mct_match_table[] = {
> +	{ .compatible = "samsung,exynos4210-mct", .data = &mct_init_spi, },
> +	{ .compatible = "samsung,exynos4412-mct", .data = &mct_init_ppi, },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, exynos4_mct_match_table);
> +
> +static struct platform_driver exynos4_mct_driver = {
> +	.probe		= exynos4_mct_probe,
> +	.driver		= {
> +		.name	= "exynos-mct",
> +		.of_match_table = exynos4_mct_match_table,
> +	},
> +};
> +module_platform_driver(exynos4_mct_driver);
> +
> +MODULE_DESCRIPTION("Exynos Multi Core Timer Driver");
> +MODULE_LICENSE("GPL");


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Re: [PATCH v4 3/6] clocksource/drivers/exynos_mct: Set local timer interrupts as percpu

[Marek Szyprowski]

On 20.06.2025 20:17, Will McVicker wrote:
> From: Hosung Kim <hosung0.kim@samsung.com>
>
> To allow the CPU to handle it's own clock events, we need to set the
> IRQF_PERCPU flag. This prevents the local timer interrupts from
> migrating to other CPUs.
>
> Signed-off-by: Hosung Kim <hosung0.kim@samsung.com>
> [Original commit from https://android.googlesource.com/kernel/gs/+/03267fad19f093bac979ca78309483e9eb3a8d16]
> Reviewed-by: Peter Griffin <peter.griffin@linaro.org>
> Reviewed-by: Youngmin Nam <youngmin.nam@samsung.com>
> Tested-by: Youngmin Nam <youngmin.nam@samsung.com>
> Signed-off-by: Will McVicker <willmcvicker@google.com>

This patch has been merged some time ago to v6.17-rc1 as commit 
f3cec54ee3bf ("clocksource/drivers/exynos_mct: Set local timer 
interrupts as percpu"). Recently I found that it breaks CPU hotplug 
support for some 'little' cores on Exynos5422 based boards, like 
OdroidXU3/XU4:

# for i in /sys/devices/system/cpu/cpu[1-9]; do echo 0 >$i/online; done
# for i in /sys/devices/system/cpu/cpu[1-9]; do echo 1 >$i/online; done
[  117.100195] CPU2: failed to come online
-bash: echo: write error: Input/output error
[  118.140426] CPU3: failed to come online
-bash: echo: write error: Input/output error
[  118.148428] CPU4: detected I-Cache line size mismatch, workaround 
enabled
[  118.169613] CPU5: detected I-Cache line size mismatch, workaround 
enabled
[  118.216802] CPU6: detected I-Cache line size mismatch, workaround 
enabled
[  118.283725] CPU7: detected I-Cache line size mismatch, workaround 
enabled
#

Frankly speaking I have no idea why this happens. CPU hotplug was always 
broken for the CPU0, but this is not relevant for this case. Maybe this 
PERCPU flag should be applied only on ARM64-based boards to avoid 
affecting legacy ARM 32bit cases?

> ---
>   drivers/clocksource/exynos_mct.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
> index 96361d5dc57d..a5ef7d64b1c2 100644
> --- a/drivers/clocksource/exynos_mct.c
> +++ b/drivers/clocksource/exynos_mct.c
> @@ -596,7 +596,8 @@ static int __init exynos4_timer_interrupts(struct device_node *np,
>   			irq_set_status_flags(mct_irq, IRQ_NOAUTOEN);
>   			if (request_irq(mct_irq,
>   					exynos4_mct_tick_isr,
> -					IRQF_TIMER | IRQF_NOBALANCING,
> +					IRQF_TIMER | IRQF_NOBALANCING |
> +					IRQF_PERCPU,
>   					pcpu_mevt->name, pcpu_mevt)) {
>   				pr_err("exynos-mct: cannot register IRQ (cpu%d)\n",
>   									cpu);

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland