Re: [PATCH] Lock 7 is cpuidle specific, use non-generic value for locking

From: Lina Iyer
Date: Thu Mar 12 2015 - 18:16:13 EST

On Thu, Mar 12 2015 at 15:12 -0600, Stephen Boyd wrote:
On 03/12/15 13:48, Lina Iyer wrote:
On Thu, Mar 12 2015 at 14:35 -0600, Stephen Boyd wrote:
On 03/12/15 12:38, Lina Iyer wrote:

sign off?

:) I was just hacking it to make it easier to understand. Sure.

drivers/hwspinlock/qcom_hwspinlock.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/hwspinlock/qcom_hwspinlock.c
index 93b62e0..7642524 100644
--- a/drivers/hwspinlock/qcom_hwspinlock.c
+++ b/drivers/hwspinlock/qcom_hwspinlock.c
@@ -25,16 +25,23 @@

#include "hwspinlock_internal.h"


static int qcom_hwspinlock_trylock(struct hwspinlock *lock)
struct regmap_field *field = lock->priv;
u32 lock_owner;
int ret;
+ u32 proc_id;

- ret = regmap_field_write(field, QCOM_MUTEX_APPS_PROC_ID);
+ proc_id = hwspin_lock_get_id(lock) == QCOM_CPUIDLE_LOCK ?
+ QCOM_MUTEX_CPUIDLE_OFFSET + smp_processor_id():

So we assume that the caller will always be the CPU that is locking the
lock? Also, do we assume that the remote side knows our CPU scheme here?
smp_processor_id() returns the logical CPU and not the physical CPU
number so hopefully the remote side doesn't care about logical CPU
numbers being written to the lock value.

The remote side (SCM) doesnt care the value written. We use 128+cpu to
be unique in Linux(128 is to make sure it doesnt clash with predefined
values used across by other processors.

It looks like the remote side unlocks it too? It doesn't seem like this
will work with the framework very well. The framework has a kernel
spinlock attached to the hwspinlock so when we lock the hwspinlock we
also lock the kernel spinlock and we only release the kernel spinlock
when the kernel unlocks the hwspinlock. In this case it seems like
cpuidle wants to have it's own kernel spinlock and just use the trylock
loop part of __hwspin_lock_timeout() without taking any kernel side
locks. Plus it wants to write a specific value to the lock.

Just noticed that part of the hwspinlock. Yes SCM unlocks the
hwspinlock. So I cannot hold any lock in Linux. May need changes in the
hwspinlock framework. Seems like an additional flag in hwspinlock to not
lock any in the trylock path work work. Hmm....

Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at