[PATCH v2 2/6] iommu/arm-smmu: Add interconnect bandwidth voting support

[Dmitry Baryshkov]

On Mon, Jun 08, 2026 at 06:59:34PM +0530, Bibek Kumar Patro wrote:
> 
> ...
> 
> > ---
> >   drivers/iommu/arm/arm-smmu/arm-smmu.c | 57 +++++++++++++++++++++++++++++++++--
> >   drivers/iommu/arm/arm-smmu/arm-smmu.h |  2 ++
> >   2 files changed, 57 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > index 0bd21d206eb3e75c3b9fb1364cdc92e82c5aa499..07c7e44ec6a5bd1488f00f87d859a20495e46601 100644
> > --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > @@ -53,6 +53,11 @@
> >   #define MSI_IOVA_BASE			0x8000000
> >   #define MSI_IOVA_LENGTH			0x100000
> > +/* Interconnect bandwidth vote values for the SMMU register access path */
> > +#define ARM_SMMU_ICC_AVG_BW		0
> > +#define ARM_SMMU_ICC_PEAK_BW_HIGH	1000
> > +#define ARM_SMMU_ICC_PEAK_BW_LOW	0
> > +
> >   static int force_stage;
> >   module_param(force_stage, int, S_IRUGO);
> >   MODULE_PARM_DESC(force_stage,
> > @@ -86,6 +91,36 @@ static inline void arm_smmu_rpm_put(struct arm_smmu_device *smmu)
> >   	}
> >   }
> > +static int arm_smmu_icc_get(struct arm_smmu_device *smmu)
> > +{
> > +	smmu->icc_path = devm_of_icc_get(smmu->dev, NULL);
> > +	if (IS_ERR(smmu->icc_path)) {
> > +		int err = PTR_ERR(smmu->icc_path);
> > +
> > +		if (err == -ENODEV) {
> > +			smmu->icc_path = NULL;
> > +			return 0;
> > +		}
> > +		return dev_err_probe(smmu->dev, err,
> > +				     "failed to get interconnect path\n");
> > +	}
> > +	return 0;
> > +}
> > +
> > +static void arm_smmu_icc_enable(struct arm_smmu_device *smmu)
> > +{
> > +	if (smmu->icc_path)
> > +		WARN_ON(icc_set_bw(smmu->icc_path, ARM_SMMU_ICC_AVG_BW,
> > +				   ARM_SMMU_ICC_PEAK_BW_HIGH));
> > +}
> > +
> > +static void arm_smmu_icc_disable(struct arm_smmu_device *smmu)
> > +{
> > +	if (smmu->icc_path)
> > +		WARN_ON(icc_set_bw(smmu->icc_path, ARM_SMMU_ICC_AVG_BW,
> > +				   ARM_SMMU_ICC_PEAK_BW_LOW));
> > +}
> > +
> >   static void arm_smmu_rpm_use_autosuspend(struct arm_smmu_device *smmu)
> >   {
> >   	/*
> > @@ -2189,6 +2224,17 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
> >   	if (err)
> >   		return err;
> > +	/*
> > +	 * Acquire and vote the interconnect path before accessing any SMMU
> > +	 * registers (including ARM_SMMU_GR0_ID0 in arm_smmu_device_cfg_probe).
> > +	 */
> > +	err = arm_smmu_icc_get(smmu);
> > +	if (err) {
> > +		clk_bulk_disable_unprepare(smmu->num_clks, smmu->clks);
> > +		return err;
> > +	}
> > +	arm_smmu_icc_enable(smmu);
> > +
> >   	err = arm_smmu_device_cfg_probe(smmu);
> >   	if (err)
> >   		return err;
> > @@ -2273,8 +2319,10 @@ static void arm_smmu_device_shutdown(struct platform_device *pdev)
> >   	if (pm_runtime_enabled(smmu->dev))
> >   		pm_runtime_force_suspend(smmu->dev);
> > -	else
> > +	else {
> >   		clk_bulk_disable(smmu->num_clks, smmu->clks);
> > +		arm_smmu_icc_disable(smmu);
> > +	}
> >   	clk_bulk_unprepare(smmu->num_clks, smmu->clks);
> >   }
> > @@ -2294,9 +2342,13 @@ static int __maybe_unused arm_smmu_runtime_resume(struct device *dev)
> >   	struct arm_smmu_device *smmu = dev_get_drvdata(dev);
> >   	int ret;
> > +	arm_smmu_icc_enable(smmu);
> > +
> >   	ret = clk_bulk_enable(smmu->num_clks, smmu->clks);
> > -	if (ret)
> > +	if (ret) {
> > +		arm_smmu_icc_disable(smmu);
> >   		return ret;
> > +	}
> >   	arm_smmu_device_reset(smmu);
> > @@ -2308,6 +2360,7 @@ static int __maybe_unused arm_smmu_runtime_suspend(struct device *dev)
> >   	struct arm_smmu_device *smmu = dev_get_drvdata(dev);
> >   	clk_bulk_disable(smmu->num_clks, smmu->clks);
> > +	arm_smmu_icc_disable(smmu);
> >   	return 0;
> >   }
> > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.h b/drivers/iommu/arm/arm-smmu/arm-smmu.h
> > index 26d2e33cd328b8278888585fc07a31485d9397e2..c00606a416b2f4bb44a35e5d67f6ef801df68e1c 100644
> > --- a/drivers/iommu/arm/arm-smmu/arm-smmu.h
> > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.h
> > @@ -15,6 +15,7 @@
> >   #include <linux/bits.h>
> >   #include <linux/clk.h>
> >   #include <linux/device.h>
> > +#include <linux/interconnect.h>
> >   #include <linux/io-64-nonatomic-hi-lo.h>
> >   #include <linux/io-pgtable.h>
> >   #include <linux/iommu.h>
> > @@ -335,6 +336,7 @@ struct arm_smmu_device {
> >   	int				num_clks;
> >   	unsigned int			*irqs;
> >   	struct clk_bulk_data		*clks;
> > +	struct icc_path			*icc_path;
> >   	spinlock_t			global_sync_lock;
> > 
> 
> Any feedback or concerns on the interconnect voting approach proposed here?
> 
> This helps to address the kernel panic issue [1] reported for one of
> Qualcomm platforms.

Please respond or tend the issues, pointed out by Sashiko.

> 
> [1]: https://github.com/qualcomm-linux/kernel/issues/297
> 
> Thanks,
> Bibek

-- 
With best wishes
Dmitry