linux-kernel - Re: [PATCH v3 2/3] dt-bindings: arm: hisilicon: Add binding for L3 cache controller

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Date:   Tue, 12 Jan 2021 20:35:50 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Arnd Bergmann <arnd@...nel.org>
CC:     Russell King <rmk+kernel@....linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        "Haojian Zhuang" <haojian.zhuang@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh+dt@...nel.org>,
        Wei Xu <xuwei5@...ilicon.com>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/3] dt-bindings: arm: hisilicon: Add binding for L3
 cache controller



On 2021/1/12 16:46, Arnd Bergmann wrote:
> On Tue, Jan 12, 2021 at 2:56 AM Zhen Lei <thunder.leizhen@...wei.com> wrote:
> 
>> +---
>> +$id: http://devicetree.org/schemas/arm/hisilicon/l3cache.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Hisilicon L3 cache controller
>> +
>> +maintainers:
>> +  - Wei Xu <xuwei5@...ilicon.com>
>> +
>> +description: |
>> +  The Hisilicon L3 outer cache controller supports a maximum of 36-bit physical
>> +  addresses. The data cached in the L3 outer cache can be operated based on the
>> +  physical address range or the entire cache.
>> +
>> +properties:
>> +  compatible:
>> +    items:
>> +      - const: hisilicon,l3cache
>> +
> 
> The compatible string needs to be a little more specific, I'm sure
> you cannot guarantee that this is the only L3 cache controller ever
> designed in the past or future by HiSilicon.
> 
> Normally when you have an IP block that is itself unnamed but that is specific
> to one or a few SoCs but that has no na, the convention is to include the name
> of the first SoC that contained it.

Right, thanks for your suggestion, I will rename it to "hisilicon,hi1381-l3cache"
and "hisilicon,hi1215-l3cache".

> 
> Can you share which products actually use this L3 cache controller?

This L3 cache controller is used on Hi1381 and Hi1215 board. I don't know where
these two boards are used. Our company is too large. Software is delivered level
by level. I'm only involved in the Kernel-related part.

> 
> On a related note, what does the memory map look like on this chip?

memory@...000 {
     device_type = "memory";
     reg = <0x0 0xa00000 0x0 0x1aa00000>, <0x1 0xe0000000 0x0 0x1d000000>, <0x0 0x1f400000 0x0 0xb5c00000>;
};

Currently, the DTS is being maintained by ourselves, I'll try to upstream it later.

> Do you support more than 4GB of total installed memory? If you

Currently, the total size does not exceed 4 GB. However, the physical address is wider than 32 bits.

> do, this becomes a problem in the future as highmem support
> winds down. In fact  anything more than 1GB on a 32-bit system
> requires more work on the kernel to be completed before we remove
> highmem, and will incur a slowdown. If the total is under 4GB but the
> memory is not in a contiguous physical address range. See my
> Linaro connect presentation[1] for further information on the topic.

Great.

> 
>        Arnd
> 
> [1] https://connect.linaro.org/resources/lvc20/lvc20-106/
> 
> .
>