linux-kernel - Re: [PATCH v2 11/29] arm_mpam: Probe hardware to find the supported partid/pmg values

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Message-ID: <0382ea8a-8f15-4983-8659-0471f9090012@arm.com>
Date: Fri, 12 Sep 2025 12:11:03 +0100
From: Ben Horgan <ben.horgan@....com>
To: James Morse <james.morse@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org
Cc: D Scott Phillips OS <scott@...amperecomputing.com>,
 carl@...amperecomputing.com, lcherian@...vell.com,
 bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
 baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
 Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
 dfustini@...libre.com, amitsinght@...vell.com,
 David Hildenbrand <david@...hat.com>, Dave Martin <dave.martin@....com>,
 Koba Ko <kobak@...dia.com>, Shanker Donthineni <sdonthineni@...dia.com>,
 fenghuay@...dia.com, baisheng.gao@...soc.com,
 Jonathan Cameron <jonathan.cameron@...wei.com>, Rob Herring
 <robh@...nel.org>, Rohit Mathew <rohit.mathew@....com>,
 Rafael Wysocki <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo
 <guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH v2 11/29] arm_mpam: Probe hardware to find the supported
 partid/pmg values

Hi James,

On 9/10/25 21:42, James Morse wrote:
> CPUs can generate traffic with a range of PARTID and PMG values,
> but each MSC may also have its own maximum size for these fields.
> Before MPAM can be used, the driver needs to probe each RIS on
> each MSC, to find the system-wide smallest value that can be used.
> The limits from requestors (e.g. CPUs) also need taking into account.
> 
> While doing this, RIS entries that firmware didn't describe are created
> under MPAM_CLASS_UNKNOWN.
> 
> While we're here, implement the mpam_register_requestor() call
> for the arch code to register the CPU limits. Future callers of this
> will tell us about the SMMU and ITS.
> 
> Signed-off-by: James Morse <james.morse@....com>
> ---
> Changes since v1:
>  * Change to lock ordering now that the list-lock mutex isn't held from
>    the cpuhp call.
>  * Removed irq-unmaksed assert in requestor register.
>  * Changed captialisation in print message.
> ---
>  drivers/resctrl/mpam_devices.c  | 150 +++++++++++++++++++++++++++++++-
>  drivers/resctrl/mpam_internal.h |   6 ++
>  include/linux/arm_mpam.h        |  14 +++
>  3 files changed, 169 insertions(+), 1 deletion(-)

Looks good to me. I think Jonathan's comment on getting rid of the local
variable, 'found', is worthwhile.

Reviewed-by: Ben Horgan <ben.horgan@....com>

Thanks,

Ben