linux-kernel - Re: [PATCHv1 4/5] arm64: dts: amlogic: Add cache information to the Amlogic S922X SoC

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Message-ID: <f87069a4-042c-467a-94fb-0b65bfa4758d@linaro.org>
Date: Tue, 6 Feb 2024 16:01:45 +0100
From: neil.armstrong@...aro.org
To: Anand Moon <linux.amoon@...il.com>
Cc: Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Kevin Hilman <khilman@...libre.com>,
 Jerome Brunet <jbrunet@...libre.com>,
 Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv1 4/5] arm64: dts: amlogic: Add cache information to the
 Amlogic S922X SoC

On 06/02/2024 11:15, Anand Moon wrote:
> Hi Neil,
> 
> On Tue, 6 Feb 2024 at 14:30, Neil Armstrong <neil.armstrong@...aro.org> wrote:
>>
>> On 05/02/2024 18:19, Anand Moon wrote:
>>> As per S922X datasheet add missing cache information to the Amlogic
>>> S922X SoC.
>>>
>>> - Each Cortex-A53 core has 32 KB of instruction cache and
>>>        32 KB of L1 data cache available.
>>> - Each Cortex-A73 core has 64 KB of L1 instruction cache and
>>>        64 KB of L1 data cache available.
>>> - The little (A53) cluster has 512 KB of unified L2 cache available.
>>> - The big (A73) cluster has 1 MB of unified L2 cache available.
>>
>> Datasheet says:
>> The quad core Cortex™-A73 processor is paired with A53 processor in a big.Little configuration, with each
>> core has L1 instruction and data chaches, together with a single shared L2 unified cache with A53
>>
> Ok,
> 
> Since all the Cortex™-A73 and Cortex™-A53 share some improvements in
> the architecture with some improvements in cache features
> hence I update the changes accordingly.
> Also, I checked this in the ARM documentation earlier on this.

I don't understand, Amlogic states it's a shared L2 cache, but you trust
the ARM documentation instead ???

> 
>> And there's no indication of the L1 or L2 cache sizes.
> 
> What I feel is in general all the Cortex™-A73 and Cortex™-A53 supports
> L1 and L2 cache size since it is part of the core features.
> but I opted for these size values from a Wikipedia article.
> 
> On my Odroid N2+, I observe the following.
> 
> I have also done some testing on the stress-ng to verify this.


Ok I don't feel confident adding numbers that comes out of thin air,
and even more since they are only shared to userspace.

I think we should only add the numbers which are 100% sure

> 
> alarm@...hl-on2:~$ lscpu
> Architecture:           aarch64
>    CPU op-mode(s):       32-bit, 64-bit
>    Byte Order:           Little Endian
> CPU(s):                 6
>    On-line CPU(s) list:  0-5
> Vendor ID:              ARM
>    Model name:           Cortex-A53
>      Model:              4
>      Thread(s) per core: 1
>      Core(s) per socket: 2
>      Socket(s):          1
>      Stepping:           r0p4
>      CPU(s) scaling MHz: 100%
>      CPU max MHz:        1800.0000
>      CPU min MHz:        1000.0000
>      BogoMIPS:           48.00
>      Flags:              fp asimd evtstrm aes pmull sha1 sha2 crc32 cpuid
>    Model name:           Cortex-A73
>      Model:              2
>      Thread(s) per core: 1
>      Core(s) per socket: 4
>      Socket(s):          1
>      Stepping:           r0p2
>      CPU(s) scaling MHz: 63%
>      CPU max MHz:        2208.0000
>      CPU min MHz:        1000.0000
>      BogoMIPS:           48.00
>      Flags:              fp asimd evtstrm aes pmull sha1 sha2 crc32 cpuid
> Caches (sum of all):
>    L1d:                  320 KiB (6 instances)
>    L1i:                  320 KiB (6 instances)
>    L2:                   1.5 MiB (2 instances)
> NUMA:
>    NUMA node(s):         1
>    NUMA node0 CPU(s):    0-5
> Vulnerabilities:
>    Gather data sampling: Not affected
>    Itlb multihit:        Not affected
>    L1tf:                 Not affected
>    Mds:                  Not affected
>    Meltdown:             Not affected
>    Mmio stale data:      Not affected
>    Retbleed:             Not affected
>    Spec rstack overflow: Not affected
>    Spec store bypass:    Vulnerable
>    Spectre v1:           Mitigation; __user pointer sanitization
>    Spectre v2:           Vulnerable
>    Srbds:                Not affected
>    Tsx async abort:      Not affected
> alarm@...hl-on2:~$
> 
> alarm@...hl-on2:~$ lstopo-no-graphics
> Machine (3659MB total)
>    Package L#0
>      NUMANode L#0 (P#0 3659MB)
>      L2 L#0 (512KB)
>        L1d L#0 (32KB) + L1i L#0 (32KB) + Core L#0 + PU L#0 (P#0)
>        L1d L#1 (32KB) + L1i L#1 (32KB) + Core L#1 + PU L#1 (P#1)
>      L2 L#1 (1024KB)
>        L1d L#2 (64KB) + L1i L#2 (64KB) + Core L#2 + PU L#2 (P#2)
>        L1d L#3 (64KB) + L1i L#3 (64KB) + Core L#3 + PU L#3 (P#3)
>        L1d L#4 (64KB) + L1i L#4 (64KB) + Core L#4 + PU L#4 (P#4)
>        L1d L#5 (64KB) + L1i L#5 (64KB) + Core L#5 + PU L#5 (P#5)
>    Block "mmcblk1boot0"
>    Block "mmcblk1boot1"
>    Block "mmcblk1"
>    Net "eth0"

This looks pretty, but let's keep exporting verified data.

> 
>   >
>> Neil
>>
> 
> Thanks
> -Anand