[PATCH AUTOSEL 4.9 05/87] gpio: gpio-omap: fix level interrupt idling

[PATCH AUTOSEL 4.9 05/87] gpio: gpio-omap: fix level interrupt idling

[Sasha Levin]

From: Russell King <rmk+kernel@armlinux.org.uk>

[ Upstream commit d01849f7deba81f4959fd9e51bf20dbf46987d1c ]

Tony notes that the GPIO module does not idle when level interrupts are
in use, as the wakeup appears to get stuck.

After extensive investigation, it appears that the wakeup will only be
cleared if the interrupt status register is cleared while the interrupt
is enabled. However, we are currently clearing it with the interrupt
disabled for level-based interrupts.

It is acknowledged that this observed behaviour conflicts with a
statement in the TRM:

CAUTION
  After servicing the interrupt, the status bit in the interrupt status
  register (GPIOi.GPIO_IRQSTATUS_0 or GPIOi.GPIO_IRQSTATUS_1) must be
  reset and the interrupt line released (by setting the corresponding
  bit of the interrupt status register to 1) before enabling an
  interrupt for the GPIO channel in the interrupt-enable register
  (GPIOi.GPIO_IRQSTATUS_SET_0 or GPIOi.GPIO_IRQSTATUS_SET_1) to prevent
  the occurrence of unexpected interrupts when enabling an interrupt
  for the GPIO channel.

However, this does not appear to be a practical problem.

Further, as reported by Grygorii Strashko <grygorii.strashko@ti.com>,
the TI Android kernel tree has an earlier similar patch as "GPIO: OMAP:
Fix the sequence to clear the IRQ status" saying:

 if the status is cleared after disabling the IRQ then sWAKEUP will not
 be cleared and gates the module transition

When we unmask the level interrupt after the interrupt has been handled,
enable the interrupt and only then clear the interrupt. If the interrupt
is still pending, the hardware will re-assert the interrupt status.

Should the caution note in the TRM prove to be a problem, we could
use a clear-enable-clear sequence instead.

Cc: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Keerthy <j-keerthy@ti.com>
Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
[tony@atomide.com: updated comments based on an earlier TI patch]
Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpio/gpio-omap.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c
index 6f9c9ac6ee70..75f30a0c418a 100644
--- a/drivers/gpio/gpio-omap.c
+++ b/drivers/gpio/gpio-omap.c
@@ -837,14 +837,16 @@ static void omap_gpio_unmask_irq(struct irq_data *d)
 	if (trigger)
 		omap_set_gpio_triggering(bank, offset, trigger);
 
-	/* For level-triggered GPIOs, the clearing must be done after
-	 * the HW source is cleared, thus after the handler has run */
-	if (bank->level_mask & BIT(offset)) {
-		omap_set_gpio_irqenable(bank, offset, 0);
+	omap_set_gpio_irqenable(bank, offset, 1);
+
+	/*
+	 * For level-triggered GPIOs, clearing must be done after the source
+	 * is cleared, thus after the handler has run. OMAP4 needs this done
+	 * after enabing the interrupt to clear the wakeup status.
+	 */
+	if (bank->level_mask & BIT(offset))
 		omap_clear_gpio_irqstatus(bank, offset);
-	}
 
-	omap_set_gpio_irqenable(bank, offset, 1);
 	raw_spin_unlock_irqrestore(&bank->lock, flags);
 }
 
-- 
2.19.1

[PATCH AUTOSEL 4.9 31/87] mmc: omap: fix the maximum timeout setting

[Sasha Levin]

From: Aaro Koskinen <aaro.koskinen@iki.fi>

[ Upstream commit a6327b5e57fdc679c842588c3be046c0b39cc127 ]

When running OMAP1 kernel on QEMU, MMC access is annoyingly noisy:

	MMC: CTO of 0xff and 0xfe cannot be used!
	MMC: CTO of 0xff and 0xfe cannot be used!
	MMC: CTO of 0xff and 0xfe cannot be used!
	[ad inf.]

Emulator warnings appear to be valid. The TI document SPRU680 [1]
("OMAP5910 Dual-Core Processor MultiMedia Card/Secure Data Memory Card
(MMC/SD) Reference Guide") page 36 states that the maximum timeout is 253
cycles and "0xff and 0xfe cannot be used".

Fix by using 0xfd as the maximum timeout.

Tested using QEMU 2.5 (Siemens SX1 machine, OMAP310), and also checked on
real hardware using Palm TE (OMAP310), Nokia 770 (OMAP1710) and Nokia N810
(OMAP2420) that MMC works as before.

[1] http://www.ti.com/lit/ug/spru680/spru680.pdf

Fixes: 730c9b7e6630f ("[MMC] Add OMAP MMC host driver")
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/mmc/host/omap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mmc/host/omap.c b/drivers/mmc/host/omap.c
index a4bf14e21b5e..21dfce21aa63 100644
--- a/drivers/mmc/host/omap.c
+++ b/drivers/mmc/host/omap.c
@@ -920,7 +920,7 @@ static inline void set_cmd_timeout(struct mmc_omap_host *host, struct mmc_reques
 	reg &= ~(1 << 5);
 	OMAP_MMC_WRITE(host, SDIO, reg);
 	/* Set maximum timeout */
-	OMAP_MMC_WRITE(host, CTO, 0xff);
+	OMAP_MMC_WRITE(host, CTO, 0xfd);
 }
 
 static inline void set_data_timeout(struct mmc_omap_host *host, struct mmc_request *req)
-- 
2.19.1

[PATCH AUTOSEL 4.9 66/87] ARM: avoid Cortex-A9 livelock on tight dmb loops

[Sasha Levin]

From: Russell King <rmk+kernel@armlinux.org.uk>

[ Upstream commit 5388a5b82199facacd3d7ac0d05aca6e8f902fed ]

machine_crash_nonpanic_core() does this:

	while (1)
		cpu_relax();

because the kernel has crashed, and we have no known safe way to deal
with the CPU.  So, we place the CPU into an infinite loop which we
expect it to never exit - at least not until the system as a whole is
reset by some method.

In the absence of erratum 754327, this code assembles to:

	b	.

In other words, an infinite loop.  When erratum 754327 is enabled,
this becomes:

1:	dmb
	b	1b

It has been observed that on some systems (eg, OMAP4) where, if a
crash is triggered, the system tries to kexec into the panic kernel,
but fails after taking the secondary CPU down - placing it into one
of these loops.  This causes the system to livelock, and the most
noticable effect is the system stops after issuing:

	Loading crashdump kernel...

to the system console.

The tested as working solution I came up with was to add wfe() to
these infinite loops thusly:

	while (1) {
		cpu_relax();
		wfe();
	}

which, without 754327 builds to:

1:	wfe
	b	1b

or with 754327 is enabled:

1:	dmb
	wfe
	b	1b

Adding "wfe" does two things depending on the environment we're running
under:
- where we're running on bare metal, and the processor implements
  "wfe", it stops us spinning endlessly in a loop where we're never
  going to do any useful work.
- if we're running in a VM, it allows the CPU to be given back to the
  hypervisor and rescheduled for other purposes (maybe a different VM)
  rather than wasting CPU cycles inside a crashed VM.

However, in light of erratum 794072, Will Deacon wanted to see 10 nops
as well - which is reasonable to cover the case where we have erratum
754327 enabled _and_ we have a processor that doesn't implement the
wfe hint.

So, we now end up with:

1:      wfe
        b       1b

when erratum 754327 is disabled, or:

1:      dmb
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        wfe
        b       1b

when erratum 754327 is enabled.  We also get the dmb + 10 nop
sequence elsewhere in the kernel, in terminating loops.

This is reasonable - it means we get the workaround for erratum
794072 when erratum 754327 is enabled, but still relinquish the dead
processor - either by placing it in a lower power mode when wfe is
implemented as such or by returning it to the hypervisior, or in the
case where wfe is a no-op, we use the workaround specified in erratum
794072 to avoid the problem.

These as two entirely orthogonal problems - the 10 nops addresses
erratum 794072, and the wfe is an optimisation that makes the system
more efficient when crashed either in terms of power consumption or
by allowing the host/other VMs to make use of the CPU.

I don't see any reason not to use kexec() inside a VM - it has the
potential to provide automated recovery from a failure of the VMs
kernel with the opportunity for saving a crashdump of the failure.
A panic() with a reboot timeout won't do that, and reading the
libvirt documentation, setting on_reboot to "preserve" won't either
(the documentation states "The preserve action for an on_reboot event
is treated as a destroy".)  Surely it has to be a good thing to
avoiding having CPUs spinning inside a VM that is doing no useful
work.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/arm/include/asm/barrier.h   | 2 ++
 arch/arm/include/asm/processor.h | 6 +++++-
 arch/arm/kernel/machine_kexec.c  | 5 ++++-
 arch/arm/kernel/smp.c            | 4 +++-
 arch/arm/mach-omap2/prm_common.c | 4 +++-
 5 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/arch/arm/include/asm/barrier.h b/arch/arm/include/asm/barrier.h
index 513e03d138ea..8331cb0d3461 100644
--- a/arch/arm/include/asm/barrier.h
+++ b/arch/arm/include/asm/barrier.h
@@ -10,6 +10,8 @@
 #define sev()	__asm__ __volatile__ ("sev" : : : "memory")
 #define wfe()	__asm__ __volatile__ ("wfe" : : : "memory")
 #define wfi()	__asm__ __volatile__ ("wfi" : : : "memory")
+#else
+#define wfe()	do { } while (0)
 #endif
 
 #if __LINUX_ARM_ARCH__ >= 7
diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
index 8a1e8e995dae..08509183c7df 100644
--- a/arch/arm/include/asm/processor.h
+++ b/arch/arm/include/asm/processor.h
@@ -77,7 +77,11 @@ extern void release_thread(struct task_struct *);
 unsigned long get_wchan(struct task_struct *p);
 
 #if __LINUX_ARM_ARCH__ == 6 || defined(CONFIG_ARM_ERRATA_754327)
-#define cpu_relax()			smp_mb()
+#define cpu_relax()						\
+	do {							\
+		smp_mb();					\
+		__asm__ __volatile__("nop; nop; nop; nop; nop; nop; nop; nop; nop; nop;");	\
+	} while (0)
 #else
 #define cpu_relax()			barrier()
 #endif
diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
index b18c1ea56bed..ef6b27fe1d2e 100644
--- a/arch/arm/kernel/machine_kexec.c
+++ b/arch/arm/kernel/machine_kexec.c
@@ -87,8 +87,11 @@ void machine_crash_nonpanic_core(void *unused)
 
 	set_cpu_online(smp_processor_id(), false);
 	atomic_dec(&waiting_for_crash_ipi);
-	while (1)
+
+	while (1) {
 		cpu_relax();
+		wfe();
+	}
 }
 
 static void machine_kexec_mask_interrupts(void)
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index bc83ec7ed53f..7a5dc011c523 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -602,8 +602,10 @@ static void ipi_cpu_stop(unsigned int cpu)
 	local_fiq_disable();
 	local_irq_disable();
 
-	while (1)
+	while (1) {
 		cpu_relax();
+		wfe();
+	}
 }
 
 static DEFINE_PER_CPU(struct completion *, cpu_completion);
diff --git a/arch/arm/mach-omap2/prm_common.c b/arch/arm/mach-omap2/prm_common.c
index f1ca9479491b..9e14604b9642 100644
--- a/arch/arm/mach-omap2/prm_common.c
+++ b/arch/arm/mach-omap2/prm_common.c
@@ -533,8 +533,10 @@ void omap_prm_reset_system(void)
 
 	prm_ll_data->reset_system();
 
-	while (1)
+	while (1) {
 		cpu_relax();
+		wfe();
+	}
 }
 
 /**
-- 
2.19.1