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

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Message-ID: <acb7ee15-f0e5-4641-a377-71205e202f15@arm.com>
Date: Fri, 14 Nov 2025 14:34:34 +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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 lcherian@...vell.com, lenb@...nel.org, linux-acpi@...r.kernel.org,
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Subject: Re: [PATCH 23/33] arm_mpam: Allow configuration to be applied and
 restored during cpu online

Hi Jonathan,

On 11/14/25 10:33, Ben Horgan wrote:
> 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.

I wasn't quite correct here. The feature bitmap for each component
indicates which features have been changed (by user configuration) to a
value different from their default. These bits aren't unset when the
setting is changed back to the reset value. It can thus be used on power
restoration to restore the user config. I think this is what James meant
by "were modified".

> 
> 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
> 
> 

-- 
Thanks,

Ben