From e2b61231aead9900431b3a097d211fd98a479d65 Mon Sep 17 00:00:00 2001
From: Alexander Boettcher <alexander.boettcher@genode-labs.com>
Date: Tue, 26 Jul 2022 14:05:01 +0200
Subject: [PATCH] pc: avoid use usleep_range in m/udelay emulation

m/udelay is called with closed interrupts. Linux contrib code expects no
other task to be run respectively to be re-scheduled. usleep_range leads to
executing other tasks, which causes assertions in "spinlock taken twice" or
"unexpected preempt count" errors, seen on runtime with wifi_drv and intel_fb.
The assertion triggered with the changes by #4562.
---
 .../intel/pc/shadow/asm/vdso/processor.h      |  6 +--
 repos/pc/src/lib/pc/lx_emul/delay.c           | 46 ++++++++++++++++---
 2 files changed, 41 insertions(+), 11 deletions(-)

diff --git a/repos/pc/src/drivers/framebuffer/intel/pc/shadow/asm/vdso/processor.h b/repos/pc/src/drivers/framebuffer/intel/pc/shadow/asm/vdso/processor.h
index db54ee6637..08414f0c1a 100644
--- a/repos/pc/src/drivers/framebuffer/intel/pc/shadow/asm/vdso/processor.h
+++ b/repos/pc/src/drivers/framebuffer/intel/pc/shadow/asm/vdso/processor.h
@@ -19,9 +19,6 @@
 #ifndef __ASSEMBLY__
 
 #include <linux/delay.h>
-#include <linux/jiffies.h>
-
-extern u64 jiffies_64;
 
 
 static __always_inline void rep_nop(void)
@@ -33,8 +30,7 @@ static __always_inline void rep_nop(void)
 static __always_inline void cpu_relax(void)
 {
 	/* break busy loop of slchi() in drivers/i2c/algos/i2c-algo-bit.c */
-	u64 const us = jiffies_to_usecs(1);
-	usleep_range(us, us);
+	__udelay(100);
 }
 
 #endif /* __ASSEMBLY__ */
diff --git a/repos/pc/src/lib/pc/lx_emul/delay.c b/repos/pc/src/lib/pc/lx_emul/delay.c
index 05d9063b6c..febbbd9a1e 100644
--- a/repos/pc/src/lib/pc/lx_emul/delay.c
+++ b/repos/pc/src/lib/pc/lx_emul/delay.c
@@ -1,6 +1,7 @@
 /*
  * \brief  Supplement for emulation for linux/include/asm-generic/delay.h
  * \author Josef Soentgen
+ * \author Alexander Boettcher
  * \date   2022-05-05
  */
 
@@ -14,21 +15,54 @@
 
 #include <asm-generic/delay.h>
 #include <linux/delay.h>
+#include <linux/jiffies.h>
 
 #include <lx_emul.h>
 
 
 void __const_udelay(unsigned long xloops)
 {
-       unsigned long usecs = xloops / 0x10C7UL;
-       if (usecs < 100)
-               lx_emul_time_udelay(usecs);
-       else
-               usleep_range(usecs, usecs * 10);
+	unsigned long const usecs = xloops / 0x10C7UL;
+	__udelay(usecs);
 }
 
 
 void __udelay(unsigned long usecs)
 {
-	lx_emul_time_udelay(usecs);
+	/*
+	 * Account for delays summing up to equivalent of 1 jiffie during
+	 * jiffies_64 stays same. When 1 jiffie is reached in sum,
+	 * increase jiffie_64 to break endless loops, seen in
+	 *  * intel_fb - cpu_relax(void) emulation used by
+	 *               busy loop of slchi() in drivers/i2c/algos/i2c-algo-bit.c
+	 *  * wifi_drv - net/wireless/intel/iwlwif* code during error code handling
+	 */
+	static uint64_t      last_jiffie = 0;
+	static unsigned long delayed_sum = 0;
+
+	if (jiffies_64 == last_jiffie) {
+		delayed_sum += usecs;
+	} else {
+		last_jiffie = jiffies_64;
+		delayed_sum = usecs;
+	}
+
+	if (usecs < 100)
+		lx_emul_time_udelay(usecs);
+	else {
+		unsigned long slept = 0;
+		while (slept < usecs) {
+			lx_emul_time_udelay(100);
+			slept += 100;
+		}
+	}
+
+	/*
+	 * When delays sum up to the equivalent of 1 jiffie,
+	 * increase it to break endless loops.
+	 */
+	if (delayed_sum >= jiffies_to_usecs(1)) {
+		jiffies_64 ++;
+		delayed_sum = 0;
+	}
 }