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

["Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>]

On 2021/1/12 21:55, Arnd Bergmann wrote:
> On Tue, Jan 12, 2021 at 1:35 PM Leizhen (ThunderTown)
> <thunder.leizhen@huawei.com> wrote:
>> On 2021/1/12 16:46, Arnd Bergmann wrote:
>>> On Tue, Jan 12, 2021 at 2:56 AM Zhen Lei <thunder.leizhen@huawei.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@hisilicon.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".

Sorry, Just received a response from the hardware developers, the SoC names need to
be changed:
hi1381 --> kunpeng509
hi1215 --> kunpeng506

So I want to rename the compatible string to "hisilicon,kunpeng-l3v1", Kunpeng L3
cache controller version 1. This is enough to distinguish other versions of cache
controller. It also facilitates the naming of the config option and files.

> 
> Sounds good.
> 
>>> 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@a00000 {
>>      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.
> 
> Ok, so it appears that the memory is actually contiguous in the first
> 3.5GB (with a few holes), plus the remaining 0.5GB being offset in
> the physical memory by 4GB (starting at 0x1e0000000 instead of
> 0xe0000000), presumably to allow the use of 32-bit DMA addresses.
> 
> This works fine for the moment, but it does require support for
> a nonlinear virt_to_phys()/phys_to_virt() translation after highmem
> gets removed, and you would get at most 3.75GB anyway, so it
> might be easier at that point to just drop the entire last block at
> 0x1e0000000, but this will depend on how well we get the 4G:4G
> code to work, and whether the users will still need kernel updates for
> this platform then.>
>      Arnd
> 
> .
>