linux-kernel - Re: [PATCH v2 00/29] arm_mpam: Add basic mpam driver

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Message-ID: <8b6e5d1e-9ccf-4f96-be31-0c51c9ed1aed@nvidia.com>
Date: Thu, 25 Sep 2025 00:18:53 -0700
From: Fenghua Yu <fenghuay@...dia.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>,
 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 00/29] arm_mpam: Add basic mpam driver


On 9/10/25 13:42, James Morse wrote:
> Hello,
>
> The major changes since v1 are:
>   * DT got ripped out - see below.
>   * The mon_sel locking was simplified - but that will come back.
>   
>   Otherwise the myriad of changes are noted on each patch.
>   
> ~
>
> This is just enough MPAM driver for ACPI. DT got ripped out. If you need DT
> support - please share your DTS so the DT folk know the binding is what is
> needed.
> This doesn't contain any of the resctrl code, meaning you can't actually drive it
> from user-space yet. Becuase of that, its hidden behind CONFIG_EXPERT.
> This will change once the user interface is connected up.
>
> This is the initial group of patches that allows the resctrl code to be built
> on top. Including that will increase the number of trees that may need to
> coordinate, so breaking it up make sense.
>
> The locking got simplified, but is still strange - this is because of the 'mpam-fb'
> firmware interface specification that is still alpha. That thing needs to wait for
> an interrupt after every system register write, which significantly impacts the
> driver. Some features just won't work, e.g. reading the monitor registers via
> perf.
>
> I've not found a platform that can test all the behaviours around the monitors,
> so this is where I'd expect the most bugs.
>
> The MPAM spec that describes all the system and MMIO registers can be found here:
> https://developer.arm.com/documentation/ddi0598/db/?lang=en
> (Ignored the 'RETIRED' warning - that is just arm moving the documentation around.
>   This document has the best overview)
>
> The expectation is this will go via the arm64 tree.
>
>
> This series is based on v6.17-rc4, and can be retrieved from:
> https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/driver/v2
>
> The rest of the driver can be found here:
> https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/snapshot/v6.17-rc4

Tested-by: Fenghua Yu <fenghuay@...dia.com>

[SNIP]

Thanks.

-Fenghua