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

[Lina Iyer]

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
> > >SoCs.
> > >
> > >Based on initial effort by Kumar Gala <galak@xxxxxxxxxxxxxx>
> > >
> > >Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxxxxxx>
> > >---
> > >
> >
> > [...]
> >
> > >+#include "hwspinlock_internal.h"
> > >+
> > >+#define QCOM_MUTEX_APPS_PROC_ID	1
> > 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?
Correct.
> > 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.
> >
> > >+#define QCOM_MUTEX_NUM_LOCKS	32
> >
> > 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;
> > >+}
> > >+
>
> --
> Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the 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  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/