linux-kernel - Re: [PATCH v3 19/29] arm_mpam: Use a static key to indicate when mpam is enabled

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Message-ID: <7ac2abe6-7311-4b20-b1fb-566ed7516315@arm.com>
Date: Mon, 20 Oct 2025 17:28:14 +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>, Jeremy Linton <jeremy.linton@....com>,
 Gavin Shan <gshan@...hat.com>
Subject: Re: [PATCH v3 19/29] arm_mpam: Use a static key to indicate when mpam
 is enabled

Hi James,

On 10/17/25 19:56, James Morse wrote:
> Once all the MSC have been probed, the system wide usable number of
> PARTID is known and the configuration arrays can be allocated.
> 
> After this point, checking all the MSC have been probed is pointless,
> and the cpuhp callbacks should restore the configuration, instead of
> just resetting the MSC.
> 
> Add a static key to enable this behaviour. This will also allow MPAM
> to be disabled in response to an error, and the architecture code to
> enable/disable the context switch of the MPAM system registers.
> 
> Signed-off-by: James Morse <james.morse@....com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
> Reviewed-by: Ben Horgan <ben.horgan@....com>
> Reviewed-by: Fenghua Yu <fenghuay@...dia.com>
> Tested-by: Fenghua Yu <fenghuay@...dia.com>
> ---
> Changes since v2:
>  * Removed the word 'TODO'.
>  * Fixed a typo in the commit message.
> ---
[..]
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index a04b09abd814..d492df9a1735 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -9,6 +9,7 @@
>  #include <linux/bitmap.h>
>  #include <linux/cpumask.h>
>  #include <linux/io.h>
> +#include <linux/jump_label.h>
>  #include <linux/llist.h>
>  #include <linux/mailbox_client.h>
>  #include <linux/mutex.h>
> @@ -19,8 +20,16 @@
>  
>  #define MPAM_MSC_MAX_NUM_RIS	16
>  
> +

nit: stray whitespace change

>  struct platform_device;
>  
> +DECLARE_STATIC_KEY_FALSE(mpam_enabled);
> +
> +static inline bool mpam_is_enabled(void)
> +{
> +	return static_branch_likely(&mpam_enabled);
> +}
> +
>  /*
>   * Structures protected by SRCU may not be freed for a surprising amount of
>   * time (especially if perf is running). To ensure the MPAM error interrupt can

-- 
Thanks,

Ben