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

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Message-ID: <20150312194325.GB31345@qualcomm.com>
Date:	Thu, 12 Mar 2015 14:43:25 -0500
From:	Andy Gross <agross@...eaurora.org>
To:	Lina Iyer <lina.iyer@...aro.org>
Cc:	Bjorn Andersson <bjorn.andersson@...ymobile.com>,
	Ohad Ben-Cohen <ohad@...ery.com>,
	linux-arm-msm@...r.kernel.org, Jeffrey Hugo <jhugo@...eaurora.org>,
	Suman Anna <s-anna@...com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/2] hwspinlock: qcom: Add support for Qualcomm HW
 Mutex block

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@...eaurora.org>
> >
> >Signed-off-by: Bjorn Andersson <bjorn.andersson@...ymobile.com>
> >---
> >
> 
> [...]
> 
> >+#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?

> 
> 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.

> >+{
> >+	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

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