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Commit f3d9ba66 authored by Liam Mark's avatar Liam Mark
Browse files

iommu/arm-smmu: lock clock enabling and reference counting 



Ensure that clock enabling and reference counting is done atomically
to avoid any potential race conditions.

An example of a potential race condition is that while thread one is
enabling the clocks thread two could enter and then exit the clock
enabling function early because of reference counting. This could
lead to thread two attempting to access registers before the clocks
are enabled.

Have removed the regulator reference because enabling the regulators
involves the use of a mutex so spin locks cannot be used to protect
the reference count. Also the use of a regulator reference count is
of limited benefit since there is only one regulator to enable.

Change-Id: I7215bbf9157907fde24c94841e347370769423c8
Signed-off-by: default avatarLiam Mark <lmark@codeaurora.org>
parent b755738d

drivers/iommu/arm-smmu.c

+16 −10
Original line number Diff line number Diff line
@@ -387,8 +387,8 @@ struct arm_smmu_device { 
	unsigned int			num_impl_def_attach_registers;



	struct mutex			atos_lock;

	atomic_t			clock_refs_count;

	atomic_t			regulator_refs_count;

	unsigned int			clock_refs_count;

	spinlock_t			clock_refs_lock;

};



struct arm_smmu_cfg {
@@ -702,9 +702,6 @@ static int arm_smmu_disable_regulators(struct arm_smmu_device *smmu) 
	if (!smmu->gdsc)

		return 0;



	if (atomic_dec_return(&smmu->regulator_refs_count) > 0)

		return 0;



	arm_smmu_unprepare_clocks(smmu);

	return regulator_disable(smmu->gdsc);

}
@@ -716,9 +713,6 @@ static int arm_smmu_enable_regulators(struct arm_smmu_device *smmu) 
	if (!smmu->gdsc)

		return 0;



	if (atomic_inc_return(&smmu->regulator_refs_count) > 1)

		return 0;



	ret = regulator_enable(smmu->gdsc);

	if (ret)

		return ret;
@@ -753,9 +747,13 @@ static void arm_smmu_disable_clocks(struct arm_smmu_device *smmu) 
static int arm_smmu_enable_clocks_atomic(struct arm_smmu_device *smmu)

{

	int i, ret = 0;

	unsigned long flags;



	if (atomic_inc_return(&smmu->clock_refs_count) > 1)

	spin_lock_irqsave(&smmu->clock_refs_lock, flags);

	if (smmu->clock_refs_count++ > 0) {

		spin_unlock_irqrestore(&smmu->clock_refs_lock, flags);

		return 0;

	}



	for (i = 0; i < smmu->num_clocks; ++i) {

		ret = clk_enable(smmu->clocks[i]);
@@ -766,6 +764,7 @@ static int arm_smmu_enable_clocks_atomic(struct arm_smmu_device *smmu) 
			break;

		}

	}

	spin_unlock_irqrestore(&smmu->clock_refs_lock, flags);

	return ret;

}
@@ -773,11 +772,17 @@ static int arm_smmu_enable_clocks_atomic(struct arm_smmu_device *smmu) 
static void arm_smmu_disable_clocks_atomic(struct arm_smmu_device *smmu)

{

	int i;

	if (atomic_dec_return(&smmu->clock_refs_count) > 0)

	unsigned long flags;



	spin_lock_irqsave(&smmu->clock_refs_lock, flags);

	if (smmu->clock_refs_count-- > 1) {

		spin_unlock_irqrestore(&smmu->clock_refs_lock, flags);

		return;

	}



	for (i = 0; i < smmu->num_clocks; ++i)

		clk_disable(smmu->clocks[i]);

	spin_unlock_irqrestore(&smmu->clock_refs_lock, flags);

}



/* Wait for any pending TLB invalidations to complete */
@@ -2288,6 +2293,7 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev) 
	smmu->dev = dev;

	mutex_init(&smmu->attach_lock);

	mutex_init(&smmu->atos_lock);

	spin_lock_init(&smmu->clock_refs_lock);



	of_id = of_match_node(arm_smmu_of_match, dev->of_node);

	if (!of_id)