Re: [PATCH v6 2/2] hwspinlock: qcom: Add support for Qualcomm HW Mutex block

From: Lina Iyer
Date: Thu Mar 12 2015 - 15:55:37 EST

On Thu, Mar 12 2015 at 13:43 -0600, Andy Gross wrote:
On Thu, Mar 12, 2015 at 01:31:50PM -0600, Lina Iyer wrote:
On Fri, Feb 27 2015 at 15:30 -0700, Bjorn Andersson wrote:
>Add driver for Qualcomm Hardware Mutex block found in many Qualcomm
>Based on initial effort by Kumar Gala <galak@xxxxxxxxxxxxxx>
>Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxxxxxx>


>+#include "hwspinlock_internal.h"
Hi Bjorn,

Not all locks use 1 to indicate its locked. For example lock index 7 is
used by cpuidle driver between HLOS and SCM. It uses a write value of
(128 + smp_processor_id()) to lock.

So this was the lock_rlock_id API?


A cpu acquires the remote spin lock, and calls into SCM to terminate the
power down sequence while passing the state of the L2. The lock help
guarantee the last core to hold the spinlock to have the most up to date
value for the L2 flush flag.


Also, talking to Jeff it seems like that out of the 32 locks defined
only 8 is accessible from Linux. So its unnecessary and probably
incorrect to assume that there are 32 locks available.

Out of curiosity, this is a TZ thing? If so, we'd expect issues if someone
decides to utilize resources that, while technically are present, are unusable
by that processor. This is not that much different from someone misconfiguring
an EE on a DMA controller.

Per Jeff, the protection unit doesnt generally allow access to locks > 8
and shouldnt be allowed and in some SoC's where they dont have the
protection, it might still be a bad idea. It would be safer to restrict to
8, than allow all 32 and hope somebody doesnt do the wrong thing.

>+ struct regmap_field *field = lock->priv;
>+ u32 lock_owner;
>+ int ret;
>+ ret = regmap_field_write(field, QCOM_MUTEX_APPS_PROC_ID);
>+ if (ret)
>+ return ret;
>+ ret = regmap_field_read(field, &lock_owner);
>+ if (ret)
>+ return ret;
>+ return lock_owner == QCOM_MUTEX_APPS_PROC_ID;

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