linux-kernel - Re: [PATCH 23/33] arm_mpam: Allow configuration to be applied and restored during cpu online

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Message-ID: <e4521b04-6c3c-418b-8cee-6be43d5ef17f@arm.com>
Date: Fri, 14 Nov 2025 10:33:12 +0000
From: Ben Horgan <ben.horgan@....com>
To: Jonathan Cameron <jonathan.cameron@...wei.com>
Cc: james.morse@....com, amitsinght@...vell.com, baisheng.gao@...soc.com,
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Subject: Re: [PATCH 23/33] arm_mpam: Allow configuration to be applied and
 restored during cpu online

Hi Jonathan,

On 11/10/25 17:27, Jonathan Cameron wrote:
> On Fri, 7 Nov 2025 12:34:40 +0000
> Ben Horgan <ben.horgan@....com> wrote:
> 
>> From: James Morse <james.morse@....com>
>>
>> When CPUs come online the MSC's original configuration should be restored.
>>
>> Add struct mpam_config to hold the configuration. This has a bitmap of
>> features that were modified. Once the maximum partid is known, allocate
> 
> I'm not following 'were modified'.  When?  Sometime in the past?
> Perhaps "features that have been modified when XXX happens" or

The intent of the features bitmp is to only update the configuration in
hardware for the feautures that require it. On reset, this is all
features, but for a user configuration change this is just the
difference from what was previously set.

However, I don't think the difference part is currently working
correctly; the bitmap always has all the bits set and so any update
configures everything. I'll look into this.

> 
> Having read the code I think this is something like "are modified as configuration
> is read".
> 
>> a configuration array for each component, and reprogram each RIS
>> configuration from this.
Thanks,

Ben