Re: [PATCH DNM v3 8/8] arm64: dts: qcom: kaanapali: Add MPAM MSC nodes for the L2 caches

[Yin Li <yin.li@oss.qualcomm.com>]

On 10/12/2026 7:27 PM, Ben Horgan wrote:
> Hi Yin,
> 
> On 12/10/2026 11:48, Yin Li wrote:
>>
>>
>> On 10/9/2026 5:00 AM, Rob Herring wrote:
>>> On Thu, Oct 08, 2026 at 02:41:17PM +0800, Yin Li wrote:
>>>> Add an MPAM MSC device node for each L2 cache. Each MSC is nested
>>>> directly under its L2 cache node so that the cache node is the MSC's
>>>> parent device and its CPU affinity is derived from that cache.
>>>>
>>>> The L2 cache nodes are placed directly under the root node. The root is
>>>> the root of the physical address space, so each cache node only needs an
>>>> identity 'ranges' property for its nested MSC's 'reg' to be resolved to
>>>> a physical address. The two caches use distinct node names (l2-cache-0
>>>> and l2-cache-1) since a cache node has no MMIO unit-address of its own.
>>>>
>>>> The nodes are disabled by default. Production firmware does not expose
>>>> MSC register access to the OS, so these nodes can only be enabled on a
>>>> local test setup where firmware permits direct MMIO access to the MSCs.
>>>> This DTS is therefore only an example for other platform DT authors and
>>>> is not intended to be merged.
>>>>
>>>> Co-developed-by: Huang Yiwei <huang.yiwei@oss.qualcomm.com>
>>>> Signed-off-by: Huang Yiwei <huang.yiwei@oss.qualcomm.com>
>>>> Signed-off-by: Yin Li <yin.li@oss.qualcomm.com>
>>>> ---
>>>>    arch/arm64/boot/dts/qcom/kaanapali.dtsi | 50 +++++++++++++++++++++++++--------
>>>>    1 file changed, 38 insertions(+), 12 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/boot/dts/qcom/kaanapali.dtsi b/arch/arm64/boot/dts/qcom/kaanapali.dtsi
>>>> index 131fd2a16c54..b1dcb1e9c570 100644
>>>> --- a/arch/arm64/boot/dts/qcom/kaanapali.dtsi
>>>> +++ b/arch/arm64/boot/dts/qcom/kaanapali.dtsi
> 
> [...]
> 
>>
>>>> +
>>>> +        msc@19870000 {
>>>> +            compatible = "arm,mpam-msc";
>>>> +            reg = <0x0 0x19870000 0x0 0x10000>;
>>>
>>> The MPAM register length is 0x321C.
>>>
>>
>> You are right, the MPAM register space is 0x321c per the specification.
>> Will update accordingly.
> 
> That is the full extent but truncation is allowed by the architecture.
> 
> Section B.9 9.2.3 Permitted truncation of an MPAM feature page IQGXFF it mentions
> some conditions but these haven't been updated for the introduction of FEAT_MPAM_MSC_DOMAINS.
> 
> Does your implementation have domains?
> 

Hi Ben,

Our implementation does not have domains. So 0x321c reflects the full 
feature page for MSC.

Thanks,
Yin


> Thanks,
> 
> Ben
> 
> 
>>
>> Thanks,
>> Yin
>>
>>> Rob
>>
> 

-- 
Thx and BRs,
Yin