[PATCH v8 2/2] iommu/riscv: create a auxiliary device for HPM

[Nutty.Liu]

On 9/4/2026 5:21 PM, Zong Li wrote:
> Create an auxiliary device for HPM when the IOMMU supports a
> hardware performance monitor.
>
> Tested-by: Chen Pei <cp0613 at linux.alibaba.com>
> Tested-by: Fangyu Yu <fangyu.yu at linux.alibaba.com>
> Reviewed-by: Guo Ren <guoren at kernel.org>
> Reviewed-by: Yicong Yang <yang.yicong at picoheart.com>
> Suggested-by: Samuel Holland <samuel.holland at sifive.com>
> Signed-off-by: Zong Li <zong.li at sifive.com>
Reviewed-by: Nutty Liu <nutty.liu at hotmail.com>

Thanks,
Nutty
> ---
>   drivers/iommu/riscv/Kconfig |  1 +
>   drivers/iommu/riscv/iommu.c | 37 +++++++++++++++++++++++++++++++++++++
>   2 files changed, 38 insertions(+)
>
> diff --git a/drivers/iommu/riscv/Kconfig b/drivers/iommu/riscv/Kconfig
> index b86e5ab94183..8025bf0fb67f 100644
> --- a/drivers/iommu/riscv/Kconfig
> +++ b/drivers/iommu/riscv/Kconfig
> @@ -10,6 +10,7 @@ config RISCV_IOMMU
>   	select GENERIC_PT
>   	select IOMMU_PT
>   	select IOMMU_PT_RISCV64
> +	select AUXILIARY_BUS
>   	help
>   	  Support for implementations of the RISC-V IOMMU architecture that
>   	  complements the RISC-V MMU capabilities, providing similar address
> diff --git a/drivers/iommu/riscv/iommu.c b/drivers/iommu/riscv/iommu.c
> index cec3ddd7ab10..7f619971bb70 100644
> --- a/drivers/iommu/riscv/iommu.c
> +++ b/drivers/iommu/riscv/iommu.c
> @@ -14,6 +14,7 @@
>   
>   #include <linux/acpi.h>
>   #include <linux/acpi_rimt.h>
> +#include <linux/auxiliary_bus.h>
>   #include <linux/compiler.h>
>   #include <linux/crash_dump.h>
>   #include <linux/init.h>
> @@ -48,6 +49,9 @@
>   static DEFINE_IDA(riscv_iommu_pscids);
>   #define RISCV_IOMMU_MAX_PSCID		(BIT(20) - 1)
>   
> +/* IOMMU PMU auxiliary device id allocation namespace. */
> +static DEFINE_IDA(riscv_iommu_pmu_ida);
> +
>   /* Device resource-managed allocations */
>   struct riscv_iommu_devres {
>   	void *addr;
> @@ -565,6 +569,36 @@ static irqreturn_t riscv_iommu_fltq_process(int irq, void *data)
>   	return IRQ_HANDLED;
>   }
>   
> +/*
> + * IOMMU Hardware performance monitor
> + */
> +static void riscv_iommu_pmu_id_free(void *data)
> +{
> +	ida_free(&riscv_iommu_pmu_ida, (unsigned long)data);
> +}
> +
> +static int riscv_iommu_hpm_enable(struct riscv_iommu_device *iommu)
> +{
> +	struct auxiliary_device *auxdev;
> +	int id, ret;
> +
> +	id = ida_alloc(&riscv_iommu_pmu_ida, GFP_KERNEL);
> +	if (id < 0)
> +		return id;
> +
> +	ret = devm_add_action_or_reset(iommu->dev, riscv_iommu_pmu_id_free,
> +				       (void *)(unsigned long)id);
> +	if (ret)
> +		return ret;
> +
> +	auxdev = __devm_auxiliary_device_create(iommu->dev, "riscv-iommu",
> +						"pmu", iommu, id);
> +	if (!auxdev)
> +		return -ENODEV;
> +
> +	return 0;
> +}
> +
>   /* Lookup and initialize device context info structure. */
>   static struct riscv_iommu_dc *riscv_iommu_get_dc(struct riscv_iommu_device *iommu,
>   						 unsigned int devid)
> @@ -1613,6 +1647,9 @@ int riscv_iommu_init(struct riscv_iommu_device *iommu)
>   		goto err_remove_sysfs;
>   	}
>   
> +	if (iommu->caps & RISCV_IOMMU_CAPABILITIES_HPM)
> +		riscv_iommu_hpm_enable(iommu);
> +
>   	return 0;
>   
>   err_remove_sysfs: