[RFC PATCH 5/7] iommu/riscv: Expose global QoS IDs in sysfs

[Zhanpeng Zhang]

Hi Drew,

On 8/12/26 5:21 AM, Drew Fustini wrote:
> On Tue, Jul 14, 2026 at 09:06:55PM +0800, Zhanpeng Zhang wrote:
>> The RISC-V IOMMU QoS extension provides iommu_qosid as a per-IOMMU
>> global default tag. It is used for IOMMU-originated DDT, CQ, FQ, PQ, and
>> MSI accesses, and for device-originated requests when DDTP is in BARE
>> mode.
>>
>> Initialize iommu_qosid to RCID 0 and MCID 0 when the hardware advertises
>> QOSID support. Preserve reserved and WPRI bits with read-modify-write,
>> and use register readback to reject values which the WARL fields do not
>> retain.
>>
>> Add a qosid attribute to the RISC-V IOMMU class device. Reading returns
>> the current RCID and MCID values. Writing the documented
>> 'rcid=<rcid> mcid=<mcid>' form updates both fields while preserving the
>> other register bits.
>>
>> Keep this interface separate from resctrl group QoS. The sysfs attribute
>> controls the IOMMU-wide default, while resctrl device assignment programs
>> per-device DC.ta in translated modes.
>>
>> Signed-off-by: Zhanpeng Zhang <zhangzhanpeng.jasper at bytedance.com>
>> ---
>>   .../ABI/testing/sysfs-class-iommu-riscv-iommu |  27 +++
>>   MAINTAINERS                                   |  10 ++
>>   drivers/iommu/riscv/iommu.c                   | 159 +++++++++++++++++-
>>   drivers/iommu/riscv/iommu.h                   |   9 +-
>>   4 files changed, 202 insertions(+), 3 deletions(-)
>>   create mode 100644 Documentation/ABI/testing/sysfs-class-iommu-riscv-iommu
> [..]
>> diff --git a/drivers/iommu/riscv/iommu.h b/drivers/iommu/riscv/iommu.h
>> index 2c57625637bf..13ea67b7e42d 100644
>> --- a/drivers/iommu/riscv/iommu.h
>> +++ b/drivers/iommu/riscv/iommu.h
>> @@ -12,8 +12,12 @@
>>   #define _RISCV_IOMMU_H_
>>
>>   #include <linux/iommu.h>
>> -#include <linux/types.h>
>>   #include <linux/iopoll.h>
>> +#include <linux/mutex.h>
>> +#include <linux/types.h>
>> +#ifdef CONFIG_RISCV_IOMMU_32BIT
>> +#include <linux/spinlock.h>
>> +#endif
>
> RISCV_IOMMU_32BIT does not seem to exist upstream and these lines
> to just be deleted later in patch 6.
>
>
> Drew

Oops. These lines are leftovers from downstream code. I'll fix that.

Thanks,
Zhanpeng