Date:   Thu, 18 May 2023 20:29:04 +0800
From:   "lihuisong (C)" <lihuisong@...wei.com>
To:     Sudeep Holla <sudeep.holla@....com>
CC:     Arnd Bergmann <arnd@...db.de>,
        Bjorn Andersson <andersson@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Shawn Guo <shawnguo@...nel.org>,
        <linux-kernel@...r.kernel.org>, <soc@...nel.org>,
        <wanghuiqiang@...wei.com>, <tanxiaofei@...wei.com>,
        <liuyonglong@...wei.com>, <huangdaode@...wei.com>,
        <linux-acpi@...r.kernel.org>, Len Brown <lenb@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        <devicetree@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Subject: Re: [PATCH] soc: hisilicon: Support HCCS driver on Kunpeng SoC


在 2023/5/18 16:38, Sudeep Holla 写道:
> On Thu, May 18, 2023 at 04:24:36PM +0800, lihuisong (C) wrote:
>> 在 2023/5/17 21:16, Sudeep Holla 写道:
>>> On Wed, May 17, 2023 at 07:35:25PM +0800, lihuisong (C) wrote:
>>>> 在 2023/5/17 17:30, Sudeep Holla 写道:
>>>>> On Wed, May 17, 2023 at 03:16:12PM +0800, lihuisong (C) wrote:
>>>>>
>>>>> [...]
>>>>>
>>>>>> No. I want to use this flag to make compability between different platforms.
>>>>>> This driver only use PCC OpRegion to access to the channel if platform
>>>>>> support use PCC OpRegion.
>>>>> What do you mean by that ? It is not correct. If there is a PCC Opregion,
>>>>> then you need to make it work with drivers/acpi/acpi_pcc.c
>>>>>
>>>>> You need to have all the other details in the firmware(ASL). By looking
>>>>> at the driver, it has no connection to PCC Opregion IMO unless I am missing
>>>>> something.
>>>> Driver just needs to call these APIs, such as acpi_evaluate_integer(), if
>>>> want to use PCC OpRegion.
>>> OK, please provide examples. I am definitely lost as it doesn't match with
>>> my understanding of how PCC Opregions are/can be used.
>>>
>>>> I know that. I have tested PCC OpRegion before.
>>> Cool, examples please.
>>>
>>>> You've completely misunderstood what I said.😅
>>>>
>>> Hmm, may be but I need examples.
>> As you said below, the driver works just for PCC not PCC Opregion for now.
>> not sure if we need to discuss how PCC Opregion is used here.
> Good let us drop the idea of using PCC Opregion with this driver for now.
>
>>>> I mean that this driver plans to support both PCC and PCC OpRegion.
>>>> For example,
>>>> Platform A: this driver use PCC (as the current implementation)
>>> Good, then just keep what it needs in the implementation nothing more
>>> until you add support for something you have described below(not that
>>> I agree, just want you to make progress here based on what is actually
>>> required today)
>> Agreed.
>>>> Platform B: this driver use PCC OpRegion (Currently, this patch does not
>>>> implement it, but it may be available in the future.)
>>> Then let us discuss that in the future, don't add unnecessary complexity
>>> for some future use case today. You can always add it when you introduce
>>> that feature or support in the future.
>> Yes. We just need to focus on the current.
>> If there are any usage problems with PCC OpRegion in the future, we can
>> discuss that later.
>>
> Agreed.
>
>> My original full scheme is as follows:
>> -->
>> dev_flags = get_device_flags();  // to know if use PCC OpRegion
>> if (USE_PCC_OPREGION_B in dev_flags is 0) {
>>      chan_id = get_pcc_chan_id();
>>      init_mbox_client();
>>      pcc_mbox_request_channel(cl, chan_id)
>> } else {
>>      /* we need to return unsupport now because of no this feature in this
>> driver. */
>>      do_nothing();
>> }
>>
>> void get_some_info(...) {
>>      if (USE_PCC_OPREGION_B in dev_flags is 0)
>>          pcc_cmd_send();  // use PCC to communicate with Platform
>>      else
>>          acpi_evaluate_object(); // will be used in future.
>> }
>>
>> As described in the pseudocode above,
>> it is necessary to put "dev_flags" in this current driver first in case of
>> the version driver runs on the platform which just use PCC Opregion.
> No, you can't randomly define dev_flags just to assist your driver
> implementation. If you need it, you need to get the spec updated. We
> will not add anything unless that happens.
>
> Note that I don't agree with the flags at all but if you convince and get
> them added to spec, I won't object.
Ok，let us drop it.
>>>> Note:
>>>> This driver selects only one of them (PCC and PCC OpRegion) to communicate
>>>> with firmware on one platform.
>>> Let us keep it simple(KISS). The driver works just for PCC not PCC Opregion
>>> for now.
>> ok.
> Good
>
>>>> We use one bit in device-flags to know which one this driver will use.
>>>>
>>> NACK again just to re-iterate my point if you have not yet accepted that
>>> fact.
>> Above is our plan. Do you still think we shouldn't add this device-flags?
>> please let me know.
> Correct, no device flags as I see no use for it with your PCC only use case
> for now, right ?
Yes, it can still work well.
As for PCC Opregion way on other platform, I think of other way.
>
>>>> I'm not sure if you can understand what I mean by saing that.
>>>> If you're not confused about this now, can you reply to my last email
>>>> again?😁
>>>>
>>> The example you had IIRC is use of System Memory Opregion to demonstrate
>>> some _DSM. That has nothing to do with PCC Opregion.
>> Yes, it doesn't matter.
>> I just want to have a way to get device-flags which contains many bits(every
>> bits can be used to as one feature for expanding), rigtht?
> Get it through the spec, we don't allow random additions for some
> implementations like this.
Get it.
>>> Commit 77e2a04745ff ("ACPI: PCC: Implement OperationRegion handler for
>>> the PCC Type 3 subtype") has the example in the commit message. IIRC,
>> Your example is very useful to the user.
>>> you have even fixed couple of bugs in that driver. That is the reason
>>> why I don't understand how you think this driver and that can or must
>> Understand you, Sudeep.
>> At that time, I tested it by a simple demo driver on the platform supported
>> type3.
>>
> OK
>
>> This driver will support multiple platforms.
>> On some platforms, we can only use PCC with polling way.
>> And we will add PCC Opregion way for others platforms.
> Again when you do please post the patch with the ASL snippet as I am
> very much interested in understanding how you would make that work.
All right.
>
>> What's more, every platform just use one of them(PCC and PCC Opregion).
> OK
>
>>> work together. At least I fail to see how ATM(examples please, by that
>>> I mean ASL snippet for PCC vs PCC Opregion usage to work with this driver)
>> ok!
>> For PCC, ASL snippet is little.
>> I will add ASL snippet when this driver addes PCC Opregion way.
>
> Sounds like a plan to make progress at-least for now.
>

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