These patches try to add cpu hotplug support for Marvell BG2, BG2Q SoCs.
These SoCs can't power off cpu independently, but we still want cpu hotplug
support for them. However, we need to address "CPU still sat on kernel text"
as pointed out by Mark Rutland[1]. We achieved this by putting the dying CPU
in WFI state after the coherency is disabled, then asserting the dying CPU
reset bit to put the CPU in reset state.
patch1 use non-self-cleared control register to reset cpu. This is to prepare
for the next cpu hotplug commit.
patch2 adds the cpu hotplug support finally.
[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-May/342642.html
Jisheng Zhang (2):
arm: berlin: use non-self-cleared reset register to reset cpu
arm: berlin: add CPU hotplug support
arch/arm/mach-berlin/platsmp.c | 29 ++++++++++++++++++++++++++++-
1 file changed, 28 insertions(+), 1 deletion(-)
--
2.1.4
In Berlin SoCs, there are two kinds of cpu reset control registers: the
first one's corresponding bits will be self-cleared after some cycles,
while the second one's bits won't. Previously the first kind of reset
control register is used, this patch uses the second kind one to prepare
for the next hotplug commit.
Signed-off-by: Jisheng Zhang <[email protected]>
---
arch/arm/mach-berlin/platsmp.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/arm/mach-berlin/platsmp.c b/arch/arm/mach-berlin/platsmp.c
index 34a3753..bde327b 100644
--- a/arch/arm/mach-berlin/platsmp.c
+++ b/arch/arm/mach-berlin/platsmp.c
@@ -17,7 +17,7 @@
#include <asm/smp_plat.h>
#include <asm/smp_scu.h>
-#define CPU_RESET 0x00
+#define CPU_RESET 0x20
#define RESET_VECT 0x00
#define SW_RESET_ADDR 0x94
@@ -31,6 +31,8 @@ static inline void berlin_perform_reset_cpu(unsigned int cpu)
u32 val;
val = readl(cpu_ctrl + CPU_RESET);
+ val &= ~BIT(cpu_logical_map(cpu));
+ writel(val, cpu_ctrl + CPU_RESET);
val |= BIT(cpu_logical_map(cpu));
writel(val, cpu_ctrl + CPU_RESET);
}
--
2.1.4
Add cpu hotplug support for berlin SoCs such as BG2 and BG2Q. These SoC
don't support power off cpu independently, but we also want cpu hotplug
support in these SoCs. We achieve this goal by putting the dying CPU in
WFI state after the coherency is disabled, then asserting the dying CPU
reset bit to put the CPU in reset state.
Signed-off-by: Jisheng Zhang <[email protected]>
---
arch/arm/mach-berlin/platsmp.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff --git a/arch/arm/mach-berlin/platsmp.c b/arch/arm/mach-berlin/platsmp.c
index bde327b..c1e0540 100644
--- a/arch/arm/mach-berlin/platsmp.c
+++ b/arch/arm/mach-berlin/platsmp.c
@@ -14,6 +14,7 @@
#include <linux/of_address.h>
#include <asm/cacheflush.h>
+#include <asm/cp15.h>
#include <asm/smp_plat.h>
#include <asm/smp_scu.h>
@@ -93,8 +94,32 @@ unmap_scu:
iounmap(scu_base);
}
+#ifdef CONFIG_HOTPLUG_CPU
+static void berlin_cpu_die(unsigned int cpu)
+{
+ v7_exit_coherency_flush(louis);
+ while (1)
+ cpu_do_idle();
+}
+
+static int berlin_cpu_kill(unsigned int cpu)
+{
+ u32 val;
+
+ val = readl(cpu_ctrl + CPU_RESET);
+ val &= ~BIT(cpu_logical_map(cpu));
+ writel(val, cpu_ctrl + CPU_RESET);
+
+ return 1;
+}
+#endif
+
static struct smp_operations berlin_smp_ops __initdata = {
.smp_prepare_cpus = berlin_smp_prepare_cpus,
.smp_boot_secondary = berlin_boot_secondary,
+#ifdef CONFIG_HOTPLUG_CPU
+ .cpu_die = berlin_cpu_die,
+ .cpu_kill = berlin_cpu_kill,
+#endif
};
CPU_METHOD_OF_DECLARE(berlin_smp, "marvell,berlin-smp", &berlin_smp_ops);
--
2.1.4
On 07/07/2015 09:10 AM, Jisheng Zhang wrote:
> These patches try to add cpu hotplug support for Marvell BG2, BG2Q SoCs.
> These SoCs can't power off cpu independently, but we still want cpu hotplug
> support for them. However, we need to address "CPU still sat on kernel text"
> as pointed out by Mark Rutland[1]. We achieved this by putting the dying CPU
> in WFI state after the coherency is disabled, then asserting the dying CPU
> reset bit to put the CPU in reset state.
Jisheng,
thanks for the patches! Out of curiosity, did you measure overall SoC
power consumption with WFI and with reset respectively? I'd expect a
slightly _higher_ power consumption while in reset depending on clock
gating applied to the processor hardware.
Sebastian
> patch1 use non-self-cleared control register to reset cpu. This is to prepare
> for the next cpu hotplug commit.
>
> patch2 adds the cpu hotplug support finally.
>
>
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-May/342642.html
>
> Jisheng Zhang (2):
> arm: berlin: use non-self-cleared reset register to reset cpu
> arm: berlin: add CPU hotplug support
>
> arch/arm/mach-berlin/platsmp.c | 29 ++++++++++++++++++++++++++++-
> 1 file changed, 28 insertions(+), 1 deletion(-)
>
Dear Sebastian,
On Tue, 07 Jul 2015 09:28:34 +0200
Sebastian Hesselbarth <[email protected]> wrote:
> On 07/07/2015 09:10 AM, Jisheng Zhang wrote:
> > These patches try to add cpu hotplug support for Marvell BG2, BG2Q SoCs.
> > These SoCs can't power off cpu independently, but we still want cpu hotplug
> > support for them. However, we need to address "CPU still sat on kernel text"
> > as pointed out by Mark Rutland[1]. We achieved this by putting the dying CPU
> > in WFI state after the coherency is disabled, then asserting the dying CPU
> > reset bit to put the CPU in reset state.
>
> Jisheng,
>
> thanks for the patches! Out of curiosity, did you measure overall SoC
> power consumption with WFI and with reset respectively? I'd expect a
> slightly _higher_ power consumption while in reset depending on clock
> gating applied to the processor hardware.
Thank you for your review.
You are right. The cpu in reset state consumes a bit higher power than in WFI.
But seems we have no choice for BG2\BG2Q.
For newer Berlin SoCs than BG2Q, we support cpu power off and we'll walk through
the PSCI code path.
Thanks,
Jisheng
>
> Sebastian
>
> > patch1 use non-self-cleared control register to reset cpu. This is to prepare
> > for the next cpu hotplug commit.
> >
> > patch2 adds the cpu hotplug support finally.
> >
> >
> > [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-May/342642.html
> >
> > Jisheng Zhang (2):
> > arm: berlin: use non-self-cleared reset register to reset cpu
> > arm: berlin: add CPU hotplug support
> >
> > arch/arm/mach-berlin/platsmp.c | 29 ++++++++++++++++++++++++++++-
> > 1 file changed, 28 insertions(+), 1 deletion(-)
> >