Re: [RFC PATCH 0/7] riscv: iommu: Add QoS ID support for resctrl device assignment

[Ben Horgan <ben.horgan@arm.com>]

Hi Drew,

On 06/08/2026 06:23, Drew Fustini wrote:
> On Tue, Jul 14, 2026 at 09:06:50PM +0800, Zhanpeng Zhang wrote:
>> This RFC extends RISC-V CBQRI/resctrl support to external requesters
>> behind a RISC-V IOMMU.
> [..]
>> Open questions for this RFC:
>>
>>   * whether a common resctrl "devices" file is the right ABI for
>>     associating external requesters with a resource group;
> 
> I think a separate file is the right approach to avoid confusing iommu
> groups with pids. 
> 
> I should note that James Morse had an ARM MPAM "extras" tree [1] which
> carried an iommu_group assignment interface, using the same
> iommu_group:<id> format, but writing it to the tasks file. However, Ben
> Horgan clarified back in March [2] in a reply to Qinxin Xia that it is
> no longer maintained. Ben also wrote that the interface would likely
> change upstream. I've added Ben Horgan and Qinxin Xia to the CC list so
> hopefully they can chime in.

I haven't thought about the interface much but Reinette let me know here [1], with good reasons,
that we should consider the format of the tasks file fixed.

Thanks,

Ben

[1] https://lore.kernel.org/all/f9b08563-4958-4f3c-ad6c-1e7fa3047896@intel.com/

> 
> I plan to review the patches in this series further but I didn't want to
> delay any further in pointing out the above.
> 
> Thanks,
> Drew
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/log/?h=mpam/snapshot%2Bextras/v6.18-rc1
> [2] https://lore.kernel.org/lkml/d13fdc75-b647-44f3-9657-d592353e8a1a@huawei.com/