[PATCH 0/7] MIPS: CPS SMP fixes & improvements

[PATCH 0/7] MIPS: CPS SMP fixes & improvements

[Paul Burton]

This series includes a bunch of fixes & improvements for the MIPS SMP
code, and in particular the MIPS Coherent Processing System (CPS) SMP
implementation.

Applies atop v4.12-rc3.

Paul Burton (7):
  MIPS: Skip IPI setup if we only have 1 CPU
  MIPS: CM: Avoid per-core locking with CM3 & higher
  MIPS: CM: WARN on attempt to lock invalid VP, not BUG
  MIPS: CPS: Select CONFIG_SYS_SUPPORTS_SCHED_SMT for MIPSr6
  MIPS: CPS: Prevent multi-core with dcache aliasing
  MIPS: CPS: Handle cores not powering down more gracefully
  MIPS: CPS: Handle spurious VP starts more gracefully

 arch/mips/Kconfig          |  1 +
 arch/mips/kernel/cps-vec.S |  7 ++++++-
 arch/mips/kernel/mips-cm.c | 40 +++++++++++++++++++++++++++++++++-------
 arch/mips/kernel/smp-cps.c | 35 +++++++++++++++++++++++++++++------
 arch/mips/kernel/smp.c     |  3 +++
 5 files changed, 72 insertions(+), 14 deletions(-)

-- 
2.13.0

[PATCH 0/7] MIPS: CPS SMP fixes & improvements

[Paul Burton]

This series includes a bunch of fixes & improvements for the MIPS SMP
code, and in particular the MIPS Coherent Processing System (CPS) SMP
implementation.

Applies atop v4.12-rc3.

Paul Burton (7):
  MIPS: Skip IPI setup if we only have 1 CPU
  MIPS: CM: Avoid per-core locking with CM3 & higher
  MIPS: CM: WARN on attempt to lock invalid VP, not BUG
  MIPS: CPS: Select CONFIG_SYS_SUPPORTS_SCHED_SMT for MIPSr6
  MIPS: CPS: Prevent multi-core with dcache aliasing
  MIPS: CPS: Handle cores not powering down more gracefully
  MIPS: CPS: Handle spurious VP starts more gracefully

 arch/mips/Kconfig          |  1 +
 arch/mips/kernel/cps-vec.S |  7 ++++++-
 arch/mips/kernel/mips-cm.c | 40 +++++++++++++++++++++++++++++++++-------
 arch/mips/kernel/smp-cps.c | 35 +++++++++++++++++++++++++++++------
 arch/mips/kernel/smp.c     |  3 +++
 5 files changed, 72 insertions(+), 14 deletions(-)

-- 
2.13.0

[PATCH 1/7] MIPS: Skip IPI setup if we only have 1 CPU

[Paul Burton]

If we're running on a system with only 1 possible CPU then it makes no
sense to reserve or initialise IPIs since we'll never use them. Avoid
doing so.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---

 arch/mips/kernel/smp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
index aba1afb64b62..770d4d1516cb 100644
--- a/arch/mips/kernel/smp.c
+++ b/arch/mips/kernel/smp.c
@@ -335,6 +335,9 @@ int mips_smp_ipi_free(const struct cpumask *mask)
 
 static int __init mips_smp_ipi_init(void)
 {
+	if (num_possible_cpus() == 1)
+		return 0;
+
 	mips_smp_ipi_allocate(cpu_possible_mask);
 
 	call_desc = irq_to_desc(call_virq);
-- 
2.13.0

[PATCH 1/7] MIPS: Skip IPI setup if we only have 1 CPU

[Paul Burton]

If we're running on a system with only 1 possible CPU then it makes no
sense to reserve or initialise IPIs since we'll never use them. Avoid
doing so.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---

 arch/mips/kernel/smp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
index aba1afb64b62..770d4d1516cb 100644
--- a/arch/mips/kernel/smp.c
+++ b/arch/mips/kernel/smp.c
@@ -335,6 +335,9 @@ int mips_smp_ipi_free(const struct cpumask *mask)
 
 static int __init mips_smp_ipi_init(void)
 {
+	if (num_possible_cpus() == 1)
+		return 0;
+
 	mips_smp_ipi_allocate(cpu_possible_mask);
 
 	call_desc = irq_to_desc(call_virq);
-- 
2.13.0

[PATCH 2/7] MIPS: CM: Avoid per-core locking with CM3 & higher

[Paul Burton]

CM3 provides a GCR_CL_OTHER register per VP, rather than only per core.
This means that we don't need to prevent other VPs within a core from
racing with code that makes use of the core-other register region.

Reduce locking overhead by demoting the per-core spinlock providing
protection for CM2.5 & lower to a per-CPU/per-VP spinlock for CM3 &
higher.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---

 arch/mips/kernel/mips-cm.c | 38 ++++++++++++++++++++++++++++++++------
 1 file changed, 32 insertions(+), 6 deletions(-)

diff --git a/arch/mips/kernel/mips-cm.c b/arch/mips/kernel/mips-cm.c
index 659e6d3ae335..99bb74dd12ce 100644
--- a/arch/mips/kernel/mips-cm.c
+++ b/arch/mips/kernel/mips-cm.c
@@ -265,15 +265,34 @@ void mips_cm_lock_other(unsigned int core, unsigned int vp)
 	u32 val;
 
 	preempt_disable();
-	curr_core = current_cpu_data.core;
-	spin_lock_irqsave(&per_cpu(cm_core_lock, curr_core),
-			  per_cpu(cm_core_lock_flags, curr_core));
 
 	if (mips_cm_revision() >= CM_REV_CM3) {
 		val = core << CM3_GCR_Cx_OTHER_CORE_SHF;
 		val |= vp << CM3_GCR_Cx_OTHER_VP_SHF;
+
+		/*
+		 * We need to disable interrupts in SMP systems in order to
+		 * ensure that we don't interrupt the caller with code which
+		 * may modify the redirect register. We do so here in a
+		 * slightly obscure way by using a spin lock, since this has
+		 * the neat property of also catching any nested uses of
+		 * mips_cm_lock_other() leading to a deadlock or a nice warning
+		 * with lockdep enabled.
+		 */
+		spin_lock_irqsave(this_cpu_ptr(&cm_core_lock),
+				  *this_cpu_ptr(&cm_core_lock_flags));
 	} else {
 		BUG_ON(vp != 0);
+
+		/*
+		 * We only have a GCR_CL_OTHER per core in systems with
+		 * CM 2.5 & older, so have to ensure other VP(E)s don't
+		 * race with us.
+		 */
+		curr_core = current_cpu_data.core;
+		spin_lock_irqsave(&per_cpu(cm_core_lock, curr_core),
+				  per_cpu(cm_core_lock_flags, curr_core));
+
 		val = core << CM_GCR_Cx_OTHER_CORENUM_SHF;
 	}
 
@@ -288,10 +307,17 @@ void mips_cm_lock_other(unsigned int core, unsigned int vp)
 
 void mips_cm_unlock_other(void)
 {
-	unsigned curr_core = current_cpu_data.core;
+	unsigned int curr_core;
+
+	if (mips_cm_revision() < CM_REV_CM3) {
+		curr_core = current_cpu_data.core;
+		spin_unlock_irqrestore(&per_cpu(cm_core_lock, curr_core),
+				       per_cpu(cm_core_lock_flags, curr_core));
+	} else {
+		spin_unlock_irqrestore(this_cpu_ptr(&cm_core_lock),
+				       *this_cpu_ptr(&cm_core_lock_flags));
+	}
 
-	spin_unlock_irqrestore(&per_cpu(cm_core_lock, curr_core),
-			       per_cpu(cm_core_lock_flags, curr_core));
 	preempt_enable();
 }
 
-- 
2.13.0

[PATCH 2/7] MIPS: CM: Avoid per-core locking with CM3 & higher

[Paul Burton]

CM3 provides a GCR_CL_OTHER register per VP, rather than only per core.
This means that we don't need to prevent other VPs within a core from
racing with code that makes use of the core-other register region.

Reduce locking overhead by demoting the per-core spinlock providing
protection for CM2.5 & lower to a per-CPU/per-VP spinlock for CM3 &
higher.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---

 arch/mips/kernel/mips-cm.c | 38 ++++++++++++++++++++++++++++++++------
 1 file changed, 32 insertions(+), 6 deletions(-)

diff --git a/arch/mips/kernel/mips-cm.c b/arch/mips/kernel/mips-cm.c
index 659e6d3ae335..99bb74dd12ce 100644
--- a/arch/mips/kernel/mips-cm.c
+++ b/arch/mips/kernel/mips-cm.c
@@ -265,15 +265,34 @@ void mips_cm_lock_other(unsigned int core, unsigned int vp)
 	u32 val;
 
 	preempt_disable();
-	curr_core = current_cpu_data.core;
-	spin_lock_irqsave(&per_cpu(cm_core_lock, curr_core),
-			  per_cpu(cm_core_lock_flags, curr_core));
 
 	if (mips_cm_revision() >= CM_REV_CM3) {
 		val = core << CM3_GCR_Cx_OTHER_CORE_SHF;
 		val |= vp << CM3_GCR_Cx_OTHER_VP_SHF;
+
+		/*
+		 * We need to disable interrupts in SMP systems in order to
+		 * ensure that we don't interrupt the caller with code which
+		 * may modify the redirect register. We do so here in a
+		 * slightly obscure way by using a spin lock, since this has
+		 * the neat property of also catching any nested uses of
+		 * mips_cm_lock_other() leading to a deadlock or a nice warning
+		 * with lockdep enabled.
+		 */
+		spin_lock_irqsave(this_cpu_ptr(&cm_core_lock),
+				  *this_cpu_ptr(&cm_core_lock_flags));
 	} else {
 		BUG_ON(vp != 0);
+
+		/*
+		 * We only have a GCR_CL_OTHER per core in systems with
+		 * CM 2.5 & older, so have to ensure other VP(E)s don't
+		 * race with us.
+		 */
+		curr_core = current_cpu_data.core;
+		spin_lock_irqsave(&per_cpu(cm_core_lock, curr_core),
+				  per_cpu(cm_core_lock_flags, curr_core));
+
 		val = core << CM_GCR_Cx_OTHER_CORENUM_SHF;
 	}
 
@@ -288,10 +307,17 @@ void mips_cm_lock_other(unsigned int core, unsigned int vp)
 
 void mips_cm_unlock_other(void)
 {
-	unsigned curr_core = current_cpu_data.core;
+	unsigned int curr_core;
+
+	if (mips_cm_revision() < CM_REV_CM3) {
+		curr_core = current_cpu_data.core;
+		spin_unlock_irqrestore(&per_cpu(cm_core_lock, curr_core),
+				       per_cpu(cm_core_lock_flags, curr_core));
+	} else {
+		spin_unlock_irqrestore(this_cpu_ptr(&cm_core_lock),
+				       *this_cpu_ptr(&cm_core_lock_flags));
+	}
 
-	spin_unlock_irqrestore(&per_cpu(cm_core_lock, curr_core),
-			       per_cpu(cm_core_lock_flags, curr_core));
 	preempt_enable();
 }
 
-- 
2.13.0

[PATCH 3/7] MIPS: CM: WARN on attempt to lock invalid VP, not BUG

[Paul Burton]

Rather than using BUG_ON in the case of an invalid attempt to lock
access to a non-zero VP on a pre-CM3 system, use WARN_ON so that we have
even the slightest chance of recovery.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---

 arch/mips/kernel/mips-cm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/kernel/mips-cm.c b/arch/mips/kernel/mips-cm.c
index 99bb74dd12ce..cb0c57f860d4 100644
--- a/arch/mips/kernel/mips-cm.c
+++ b/arch/mips/kernel/mips-cm.c
@@ -282,7 +282,7 @@ void mips_cm_lock_other(unsigned int core, unsigned int vp)
 		spin_lock_irqsave(this_cpu_ptr(&cm_core_lock),
 				  *this_cpu_ptr(&cm_core_lock_flags));
 	} else {
-		BUG_ON(vp != 0);
+		WARN_ON(vp != 0);
 
 		/*
 		 * We only have a GCR_CL_OTHER per core in systems with
-- 
2.13.0

[PATCH 3/7] MIPS: CM: WARN on attempt to lock invalid VP, not BUG

[Paul Burton]

Rather than using BUG_ON in the case of an invalid attempt to lock
access to a non-zero VP on a pre-CM3 system, use WARN_ON so that we have
even the slightest chance of recovery.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---

 arch/mips/kernel/mips-cm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/kernel/mips-cm.c b/arch/mips/kernel/mips-cm.c
index 99bb74dd12ce..cb0c57f860d4 100644
--- a/arch/mips/kernel/mips-cm.c
+++ b/arch/mips/kernel/mips-cm.c
@@ -282,7 +282,7 @@ void mips_cm_lock_other(unsigned int core, unsigned int vp)
 		spin_lock_irqsave(this_cpu_ptr(&cm_core_lock),
 				  *this_cpu_ptr(&cm_core_lock_flags));
 	} else {
-		BUG_ON(vp != 0);
+		WARN_ON(vp != 0);
 
 		/*
 		 * We only have a GCR_CL_OTHER per core in systems with
-- 
2.13.0

[PATCH 4/7] MIPS: CPS: Select CONFIG_SYS_SUPPORTS_SCHED_SMT for MIPSr6

[Paul Burton]

Prior to MIPSr6 multithreading is only supported if CONFIG_MIPS_MT_SMP
is enabled, so CONFIG_MIPS_MT_SMP selects CONFIG_SYS_SUPPORTS_SCHED_SMT.
With MIPSr6 the CONFIG_MIPS_CPS SMP implementation always supports
multithreading, so have it select CONFIG_SYS_SUPPORTS_SCHED_SMT in order
to allow the scheduler to make better informed decisions on
multithreaded MIPSr6 systems (for example those using I6400 or I6500
CPUs).

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---

 arch/mips/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 2828ecde133d..a0d439cb0766 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -2369,6 +2369,7 @@ config MIPS_CPS
 	select SMP
 	select SYNC_R4K if (CEVT_R4K || CSRC_R4K)
 	select SYS_SUPPORTS_HOTPLUG_CPU
+	select SYS_SUPPORTS_SCHED_SMT if CPU_MIPSR6
 	select SYS_SUPPORTS_SMP
 	select WEAK_ORDERING
 	help
-- 
2.13.0

[PATCH 4/7] MIPS: CPS: Select CONFIG_SYS_SUPPORTS_SCHED_SMT for MIPSr6

[Paul Burton]

Prior to MIPSr6 multithreading is only supported if CONFIG_MIPS_MT_SMP
is enabled, so CONFIG_MIPS_MT_SMP selects CONFIG_SYS_SUPPORTS_SCHED_SMT.
With MIPSr6 the CONFIG_MIPS_CPS SMP implementation always supports
multithreading, so have it select CONFIG_SYS_SUPPORTS_SCHED_SMT in order
to allow the scheduler to make better informed decisions on
multithreaded MIPSr6 systems (for example those using I6400 or I6500
CPUs).

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---

 arch/mips/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 2828ecde133d..a0d439cb0766 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -2369,6 +2369,7 @@ config MIPS_CPS
 	select SMP
 	select SYNC_R4K if (CEVT_R4K || CSRC_R4K)
 	select SYS_SUPPORTS_HOTPLUG_CPU
+	select SYS_SUPPORTS_SCHED_SMT if CPU_MIPSR6
 	select SYS_SUPPORTS_SMP
 	select WEAK_ORDERING
 	help
-- 
2.13.0

[PATCH 5/7] MIPS: CPS: Prevent multi-core with dcache aliasing

[Paul Burton]

Systems using the MIPS Coherence Manager (CM) cannot support multi-core
SMP with dcache aliasing. This is because CPU caches are VIPT, but
interventions in CM-based systems provide only the physical address to
remote caches. This means that interventions may behave incorrectly in
the presence of an aliasing dcache, since the physical address used
when handling an intervention may lead to operation on an aliased cache
line rather than the correct line.

Prevent us from running into this issue by refusing to boot secondary
cores in systems where dcache aliasing may occur.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---

 arch/mips/kernel/smp-cps.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/mips/kernel/smp-cps.c b/arch/mips/kernel/smp-cps.c
index 36954ddd0b9f..90ecd099c4b0 100644
--- a/arch/mips/kernel/smp-cps.c
+++ b/arch/mips/kernel/smp-cps.c
@@ -142,9 +142,11 @@ static void __init cps_prepare_cpus(unsigned int max_cpus)
 
 	/* Warn the user if the CCA prevents multi-core */
 	ncores = mips_cm_numcores();
-	if (cca_unsuitable && ncores > 1) {
-		pr_warn("Using only one core due to unsuitable CCA 0x%x\n",
-			cca);
+	if ((cca_unsuitable || cpu_has_dc_aliases) && ncores > 1) {
+		pr_warn("Using only one core due to %s%s%s\n",
+			cca_unsuitable ? "unsuitable CCA" : "",
+			(cca_unsuitable && cpu_has_dc_aliases) ? " & " : "",
+			cpu_has_dc_aliases ? "dcache aliasing" : "");
 
 		for_each_present_cpu(c) {
 			if (cpu_data[c].core)
-- 
2.13.0

[PATCH 5/7] MIPS: CPS: Prevent multi-core with dcache aliasing

[Paul Burton]

Systems using the MIPS Coherence Manager (CM) cannot support multi-core
SMP with dcache aliasing. This is because CPU caches are VIPT, but
interventions in CM-based systems provide only the physical address to
remote caches. This means that interventions may behave incorrectly in
the presence of an aliasing dcache, since the physical address used
when handling an intervention may lead to operation on an aliased cache
line rather than the correct line.

Prevent us from running into this issue by refusing to boot secondary
cores in systems where dcache aliasing may occur.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---

 arch/mips/kernel/smp-cps.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/mips/kernel/smp-cps.c b/arch/mips/kernel/smp-cps.c
index 36954ddd0b9f..90ecd099c4b0 100644
--- a/arch/mips/kernel/smp-cps.c
+++ b/arch/mips/kernel/smp-cps.c
@@ -142,9 +142,11 @@ static void __init cps_prepare_cpus(unsigned int max_cpus)
 
 	/* Warn the user if the CCA prevents multi-core */
 	ncores = mips_cm_numcores();
-	if (cca_unsuitable && ncores > 1) {
-		pr_warn("Using only one core due to unsuitable CCA 0x%x\n",
-			cca);
+	if ((cca_unsuitable || cpu_has_dc_aliases) && ncores > 1) {
+		pr_warn("Using only one core due to %s%s%s\n",
+			cca_unsuitable ? "unsuitable CCA" : "",
+			(cca_unsuitable && cpu_has_dc_aliases) ? " & " : "",
+			cpu_has_dc_aliases ? "dcache aliasing" : "");
 
 		for_each_present_cpu(c) {
 			if (cpu_data[c].core)
-- 
2.13.0

[PATCH 6/7] MIPS: CPS: Handle cores not powering down more gracefully

[Paul Burton]

If we get into a state where a core that ought to power down isn't doing
so then the current result is that another CPU gets stuck inside
cps_cpu_die() waiting for CPU that ought to be powering down to do so.
The best case scenario is that we then trigger RCU stall messages or
lockup messages, but neither makes it particularly clear what's
happening.

Handle this more gracefully by introducing a timeout beyond which we
warn the user that the core didn't power down & stop waiting for it.
This at least allows the CPU running cps_cpu_die() to continue normally,
and hopefully presuming the CPU that powered back up is doing nothing
harmful the system will continue functioning as normal.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---

 arch/mips/kernel/smp-cps.c | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/arch/mips/kernel/smp-cps.c b/arch/mips/kernel/smp-cps.c
index 90ecd099c4b0..f832e99ad4c3 100644
--- a/arch/mips/kernel/smp-cps.c
+++ b/arch/mips/kernel/smp-cps.c
@@ -490,6 +490,7 @@ static void cps_cpu_die(unsigned int cpu)
 {
 	unsigned core = cpu_data[cpu].core;
 	unsigned int vpe_id = cpu_vpe_id(&cpu_data[cpu]);
+	ktime_t fail_time;
 	unsigned stat;
 	int err;
 
@@ -516,6 +517,7 @@ static void cps_cpu_die(unsigned int cpu)
 		 * state, the latter happening when a JTAG probe is connected
 		 * in which case the CPC will refuse to power down the core.
 		 */
+		fail_time = ktime_add_ms(ktime_get(), 2000);
 		do {
 			mips_cm_lock_other(core, 0);
 			mips_cpc_lock_other(core);
@@ -523,9 +525,28 @@ static void cps_cpu_die(unsigned int cpu)
 			stat &= CPC_Cx_STAT_CONF_SEQSTATE_MSK;
 			mips_cpc_unlock_other();
 			mips_cm_unlock_other();
-		} while (stat != CPC_Cx_STAT_CONF_SEQSTATE_D0 &&
-			 stat != CPC_Cx_STAT_CONF_SEQSTATE_D2 &&
-			 stat != CPC_Cx_STAT_CONF_SEQSTATE_U2);
+
+			if (stat == CPC_Cx_STAT_CONF_SEQSTATE_D0 ||
+			    stat == CPC_Cx_STAT_CONF_SEQSTATE_D2 ||
+			    stat == CPC_Cx_STAT_CONF_SEQSTATE_U2)
+				break;
+
+			/*
+			 * The core ought to have powered down, but didn't &
+			 * now we don't really know what state it's in. It's
+			 * likely that its _pwr_up pin has been wired to logic
+			 * 1 & it powered back up as soon as we powered it
+			 * down...
+			 *
+			 * The best we can do is warn the user & continue in
+			 * the hope that the core is doing nothing harmful &
+			 * might behave properly if we online it later.
+			 */
+			if (WARN(ktime_after(ktime_get(), fail_time),
+				 "CPU%u hasn't powered down, seq. state %u\n",
+				 cpu, stat >> CPC_Cx_STAT_CONF_SEQSTATE_SHF))
+				break;
+		} while (1);
 
 		/* Indicate the core is powered off */
 		bitmap_clear(core_power, core, 1);
-- 
2.13.0

[PATCH 6/7] MIPS: CPS: Handle cores not powering down more gracefully

[Paul Burton]

If we get into a state where a core that ought to power down isn't doing
so then the current result is that another CPU gets stuck inside
cps_cpu_die() waiting for CPU that ought to be powering down to do so.
The best case scenario is that we then trigger RCU stall messages or
lockup messages, but neither makes it particularly clear what's
happening.

Handle this more gracefully by introducing a timeout beyond which we
warn the user that the core didn't power down & stop waiting for it.
This at least allows the CPU running cps_cpu_die() to continue normally,
and hopefully presuming the CPU that powered back up is doing nothing
harmful the system will continue functioning as normal.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---

 arch/mips/kernel/smp-cps.c | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/arch/mips/kernel/smp-cps.c b/arch/mips/kernel/smp-cps.c
index 90ecd099c4b0..f832e99ad4c3 100644
--- a/arch/mips/kernel/smp-cps.c
+++ b/arch/mips/kernel/smp-cps.c
@@ -490,6 +490,7 @@ static void cps_cpu_die(unsigned int cpu)
 {
 	unsigned core = cpu_data[cpu].core;
 	unsigned int vpe_id = cpu_vpe_id(&cpu_data[cpu]);
+	ktime_t fail_time;
 	unsigned stat;
 	int err;
 
@@ -516,6 +517,7 @@ static void cps_cpu_die(unsigned int cpu)
 		 * state, the latter happening when a JTAG probe is connected
 		 * in which case the CPC will refuse to power down the core.
 		 */
+		fail_time = ktime_add_ms(ktime_get(), 2000);
 		do {
 			mips_cm_lock_other(core, 0);
 			mips_cpc_lock_other(core);
@@ -523,9 +525,28 @@ static void cps_cpu_die(unsigned int cpu)
 			stat &= CPC_Cx_STAT_CONF_SEQSTATE_MSK;
 			mips_cpc_unlock_other();
 			mips_cm_unlock_other();
-		} while (stat != CPC_Cx_STAT_CONF_SEQSTATE_D0 &&
-			 stat != CPC_Cx_STAT_CONF_SEQSTATE_D2 &&
-			 stat != CPC_Cx_STAT_CONF_SEQSTATE_U2);
+
+			if (stat == CPC_Cx_STAT_CONF_SEQSTATE_D0 ||
+			    stat == CPC_Cx_STAT_CONF_SEQSTATE_D2 ||
+			    stat == CPC_Cx_STAT_CONF_SEQSTATE_U2)
+				break;
+
+			/*
+			 * The core ought to have powered down, but didn't &
+			 * now we don't really know what state it's in. It's
+			 * likely that its _pwr_up pin has been wired to logic
+			 * 1 & it powered back up as soon as we powered it
+			 * down...
+			 *
+			 * The best we can do is warn the user & continue in
+			 * the hope that the core is doing nothing harmful &
+			 * might behave properly if we online it later.
+			 */
+			if (WARN(ktime_after(ktime_get(), fail_time),
+				 "CPU%u hasn't powered down, seq. state %u\n",
+				 cpu, stat >> CPC_Cx_STAT_CONF_SEQSTATE_SHF))
+				break;
+		} while (1);
 
 		/* Indicate the core is powered off */
 		bitmap_clear(core_power, core, 1);
-- 
2.13.0

[PATCH 7/7] MIPS: CPS: Handle spurious VP starts more gracefully

[Paul Burton]

On pre-r6 systems with the MT ASE the CPS SMP code included checks to
halt the VPE running mips_cps_boot_vpes() if its bit in the struct
core_boot_config vpe_mask field is clear. This was largely done in order
to allow us to start arbitrary VPEs within a core despite the fact that
hardware is typically configured to run only VPE0 after powering up a
core. VPE0 would start the desired other VPEs, halt itself, and the fact
that VPE0 started would be largely hidden & irrelevant.

In MIPSr6 multithreading we have control over which VPs start executing
when a core powers up via the cores CPC registers accessed remotely
through the redirect block. For this reason the MIPSr6 multithreading
path in mips_cps_boot_vpes() hasn't bothered up until now to handle
halting the VP running it.

However it is possible to power up cores entirely in hardware by using a
pwr_up pin associated with the core. Unfortunately some systems wire
this pin to a logic 1, which means that it is possible for a core to
power up at a point that software doesn't expect. The result is that we
generally go execute the kernel on a CPU that ought not to be running &
the results can be unpredictable.

Handle this case by stopping VPs that we don't expect to be running in
mips_cps_boot_vpes() - with this change even if a core powers up it will
do nothing useful & all VPs within it will stop running before they
proceed to run general kernel code & do any damage. Ideally we would
produce some sort of warning here, but given the stage of core bringup
this happens at that would be non-trivial. We also will only hit this if
a core starts up after being offlined via hotplug, and when that happens
we will already produce a warning that the CPU didn't power down in
cps_cpu_die() which seems sufficient.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org

---

 arch/mips/kernel/cps-vec.S | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/mips/kernel/cps-vec.S b/arch/mips/kernel/cps-vec.S
index a00e87b0256d..b849fe6aad94 100644
--- a/arch/mips/kernel/cps-vec.S
+++ b/arch/mips/kernel/cps-vec.S
@@ -22,6 +22,7 @@
 #define GCR_CL_COHERENCE_OFS	0x2008
 #define GCR_CL_ID_OFS		0x2028
 
+#define CPC_CL_VC_STOP_OFS	0x2020
 #define CPC_CL_VC_RUN_OFS	0x2028
 
 .extern mips_cm_base
@@ -376,8 +377,12 @@ LEAF(mips_cps_boot_vpes)
 	PTR_LI	t2, UNCAC_BASE
 	PTR_ADD	t1, t1, t2
 
-	/* Set VC_RUN to the VPE mask */
+	/* Start any other VPs that ought to be running */
 	PTR_S	ta2, CPC_CL_VC_RUN_OFS(t1)
+
+	/* Ensure this VP stops running if it shouldn't be */
+	not	ta2
+	PTR_S	ta2, CPC_CL_VC_STOP_OFS(t1)
 	ehb
 
 #elif defined(CONFIG_MIPS_MT)
-- 
2.13.0

[PATCH 7/7] MIPS: CPS: Handle spurious VP starts more gracefully

[Paul Burton]

On pre-r6 systems with the MT ASE the CPS SMP code included checks to
halt the VPE running mips_cps_boot_vpes() if its bit in the struct
core_boot_config vpe_mask field is clear. This was largely done in order
to allow us to start arbitrary VPEs within a core despite the fact that
hardware is typically configured to run only VPE0 after powering up a
core. VPE0 would start the desired other VPEs, halt itself, and the fact
that VPE0 started would be largely hidden & irrelevant.

In MIPSr6 multithreading we have control over which VPs start executing
when a core powers up via the cores CPC registers accessed remotely
through the redirect block. For this reason the MIPSr6 multithreading
path in mips_cps_boot_vpes() hasn't bothered up until now to handle
halting the VP running it.

However it is possible to power up cores entirely in hardware by using a
pwr_up pin associated with the core. Unfortunately some systems wire
this pin to a logic 1, which means that it is possible for a core to
power up at a point that software doesn't expect. The result is that we
generally go execute the kernel on a CPU that ought not to be running &
the results can be unpredictable.

Handle this case by stopping VPs that we don't expect to be running in
mips_cps_boot_vpes() - with this change even if a core powers up it will
do nothing useful & all VPs within it will stop running before they
proceed to run general kernel code & do any damage. Ideally we would
produce some sort of warning here, but given the stage of core bringup
this happens at that would be non-trivial. We also will only hit this if
a core starts up after being offlined via hotplug, and when that happens
we will already produce a warning that the CPU didn't power down in
cps_cpu_die() which seems sufficient.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org

---

 arch/mips/kernel/cps-vec.S | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/mips/kernel/cps-vec.S b/arch/mips/kernel/cps-vec.S
index a00e87b0256d..b849fe6aad94 100644
--- a/arch/mips/kernel/cps-vec.S
+++ b/arch/mips/kernel/cps-vec.S
@@ -22,6 +22,7 @@
 #define GCR_CL_COHERENCE_OFS	0x2008
 #define GCR_CL_ID_OFS		0x2028
 
+#define CPC_CL_VC_STOP_OFS	0x2020
 #define CPC_CL_VC_RUN_OFS	0x2028
 
 .extern mips_cm_base
@@ -376,8 +377,12 @@ LEAF(mips_cps_boot_vpes)
 	PTR_LI	t2, UNCAC_BASE
 	PTR_ADD	t1, t1, t2
 
-	/* Set VC_RUN to the VPE mask */
+	/* Start any other VPs that ought to be running */
 	PTR_S	ta2, CPC_CL_VC_RUN_OFS(t1)
+
+	/* Ensure this VP stops running if it shouldn't be */
+	not	ta2
+	PTR_S	ta2, CPC_CL_VC_STOP_OFS(t1)
 	ehb
 
 #elif defined(CONFIG_MIPS_MT)
-- 
2.13.0