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

[Bibek Kumar Patro <bibek.patro@oss.qualcomm.com>]

On 6/8/2026 7:20 PM, Dmitry Baryshkov wrote:
> 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.
> 

Sure, I have addressed and replied to the Sashiko warnings on v1,
I'll check on the fresh warnings on V2 along with your suggestions on 
this patch.
< I was wondering if it's needed to respond to Sashiko comments earlier 
or silently address the relevant ones,
so thanks for confirming this as well :) >

Thanks,
Bibek

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