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

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Date:	Thu, 12 Mar 2015 14:48:59 -0600
From:	Lina Iyer <lina.iyer@...aro.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	bjorn.andersson@...ymobile.com, linux-arm-msm@...r.kernel.org,
	jhugo@...eaurora.org, agross@...eaurora.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Lock 7 is cpuidle specific, use non-generic value for
 locking

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 b/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"
>>
>> -#define QCOM_MUTEX_APPS_PROC_ID	1
>> -#define QCOM_MUTEX_NUM_LOCKS	32
>> +#define QCOM_MUTEX_APPS_PROC_ID		1
>> +#define QCOM_MUTEX_CPUIDLE_OFFSET	128
>> +#define QCOM_CPUIDLE_LOCK		7
>> +#define QCOM_MUTEX_NUM_LOCKS		32
>>
>>  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.

>
>Perhaps it would be better to have a way to tell the hwspinlock
>framework what value we want written to the lock value.
>
That would be good, if there is value in that for other platforms, I
will gladly make the change.

Thoughts?

>> +			QCOM_MUTEX_APPS_PROC_ID;
>> +
>> +	ret = regmap_field_write(field, proc_id);
>>  	if (ret)
>>  		return ret;
>>
>> @@ -42,7 +49,7 @@ static int qcom_hwspinlock_trylock(struct hwspinlock *lock)
>>  	if (ret)
>>  		return ret;
>>
>> -	return lock_owner == QCOM_MUTEX_APPS_PROC_ID;
>> +	return lock_owner == proc_id;
>>  }
>>
>>  static void qcom_hwspinlock_unlock(struct hwspinlock *lock)
>
>The unlock path checks proc_id so we need to update the path there too.
>
Good point. I missed it.

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