clk: sunxi-ng: ccu_common: Replace ktime-dependent lock wait loop with udelay (#10119)

The Allwinner sunxi-ng clock control unit (CCU) driver utilizes
readl_relaxed_poll_timeout_atomic() inside ccu_helper_wait_for_lock()
to wait for PLLs to lock. This timeout loop relies internally on ktime_get()
and timekeeping APIs.

During early boot or clock transitions (such as CPUfreq DVFS scaling),
the system's clock sources and timekeeping may be unstable or temporarily
suspended. This causes ktime_get() to fail to increment or return invalid
readings, turning the timeout calculation into an infinite busy-wait loop
and triggering critical RCU stalls / kernel lockups.

Decouple the PLL lock wait loop from the timekeeping framework by replacing
the poll timeout loop with a robust, timekeeping-independent iteration loop
utilizing udelay(1) (up to 100,000 iterations / 100ms timeout limit). This
avoids timekeeping dependencies during sensitive frequency scaling operations
and prevents infinite CPU lockups when timer interrupts are suspended.


Assisted-by: Antigravity <antigravity@google.com>

Signed-off-by: Alastair D'Silva <alastair@d-silva.org>

Author: deece

patch/kernel/archive/sunxi-6.18/patches.armbian/0996-sunxi-ng-ccu-common-atomic-lock-wait.patch

@@ -0,0 +1,34 @@
+--- a/drivers/clk/sunxi-ng/ccu_common.c
++++ b/drivers/clk/sunxi-ng/ccu_common.c
+@@ -10,6 +10,7 @@
+ #include <linux/device.h>
+ #include <linux/iopoll.h>
+ #include <linux/module.h>
++#include <linux/delay.h>
+ #include <linux/slab.h>
+ 
+ #include "ccu_common.h"
+@@ -25,7 +26,7 @@
+ void ccu_helper_wait_for_lock(struct ccu_common *common, u32 lock)
+ {
+ 	void __iomem *addr;
+-	u32 reg;
++	int i;
+ 
+ 	if (!lock)
+ 		return;
+@@ -35,7 +36,14 @@
+ 	else
+ 		addr = common->base + common->reg;
+ 
+-	WARN_ON(readl_relaxed_poll_timeout(addr, reg, reg & lock, 100, 70000));
++	for (i = 0; i < 100000; i++) {
++		if (readl_relaxed(addr) & lock)
++			return;
++		udelay(1);
++	}
++	if (readl_relaxed(addr) & lock)
++		return;
++	pr_warn("%s: clock lock timeout\n", clk_hw_get_name(&common->hw));
+ }
+ EXPORT_SYMBOL_NS_GPL(ccu_helper_wait_for_lock, "SUNXI_CCU");

patch/kernel/archive/sunxi-6.18/series.conf

@@ -564,4 +564,5 @@
 	patches.armbian/drv-usb-gadget-composite-rename-serial-manufacturer.patch
 	patches.armbian/drv-video-st7796s-fb-tft-driver.patch
 	patches.armbian/include-uapi-drm_fourcc-add-ARM-tiled-format-modifier.patch
+        patches.armbian/0996-sunxi-ng-ccu-common-atomic-lock-wait.patch
         patches.armbian/0999-rtw88-sdio-fix-interrupt-storm.patch

patch/kernel/archive/sunxi-7.0/patches.armbian/0996-sunxi-ng-ccu-common-atomic-lock-wait.patch

@@ -0,0 +1,35 @@
+--- a/drivers/clk/sunxi-ng/ccu_common.c
++++ b/drivers/clk/sunxi-ng/ccu_common.c
+@@ -10,6 +10,7 @@
+ #include <linux/device.h>
+ #include <linux/iopoll.h>
+ #include <linux/module.h>
++#include <linux/delay.h>
+ #include <linux/slab.h>
+ 
+ #include "ccu_common.h"
+@@ -25,7 +26,7 @@
+ void ccu_helper_wait_for_lock(struct ccu_common *common, u32 lock)
+ {
+ 	void __iomem *addr;
+-	u32 reg;
++	int i;
+ 
+ 	if (!lock)
+ 		return;
+@@ -35,7 +36,14 @@
+ 	else
+ 		addr = common->base + common->reg;
+ 
+-	WARN_ON(readl_relaxed_poll_timeout(addr, reg, reg & lock, 25, 70000));
++	for (i = 0; i < 100000; i++) {
++		if (readl_relaxed(addr) & lock)
++			return;
++		udelay(1);
++	}
++	if (readl_relaxed(addr) & lock)
++		return;
++	pr_warn("%s: clock lock timeout\n", clk_hw_get_name(&common->hw));
+ }
+ EXPORT_SYMBOL_NS_GPL(ccu_helper_wait_for_lock, "SUNXI_CCU");
+ 

patch/kernel/archive/sunxi-7.0/series.conf

@@ -520,6 +520,7 @@
 	patches.armbian/drv-usb-gadget-composite-rename-serial-manufacturer.patch
 	patches.armbian/drv-video-st7796s-fb-tft-driver.patch
 	patches.armbian/include-uapi-drm_fourcc-add-ARM-tiled-format-modifier.patch
+	patches.armbian/0996-sunxi-ng-ccu-common-atomic-lock-wait.patch
 	patches.armbian/0997-i2c-mv64xxx-pin-runtime-pm.patch
 	patches.armbian/0998-sunxi-mmc-pin-runtime-pm.patch
 	patches.armbian/0999-rtw88-sdio-fix-interrupt-storm.patch