Date:   Mon, 18 Apr 2022 16:20:49 +0900
From:   Wangseok Lee <wangseok.lee@...sung.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>,
        robh+dt <robh+dt@...nel.org>, krzk+dt <krzk+dt@...nel.org>,
        kishon <kishon@...com>, vkoul <vkoul@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "jesper.nilsson" <jesper.nilsson@...s.com>,
        "lars.persson" <lars.persson@...s.com>
CC:     bhelgaas <bhelgaas@...gle.com>,
        linux-phy <linux-phy@...ts.infradead.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        "lorenzo.pieralisi" <lorenzo.pieralisi@....com>, kw <kw@...ux.com>,
        linux-arm-kernel <linux-arm-kernel@...s.com>,
        kernel <kernel@...s.com>, Moon-Ki Jun <moonki.jun@...sung.com>,
        Dongjin Yang <dj76.yang@...sung.com>
Subject: Re: [PATCH 0/5] Add support for Axis, ARTPEC-8 PCIe driver

> --------- Original Message ---------
> Sender : Krzysztof Kozlowski 
> Date : 2022-03-29 15:41 (GMT+09:00)
> Title : Re: [PATCH 0/5] Add support for Axis, ARTPEC-8 PCIe driver
>  
> On 29/03/2022 05:49, 이왕석 wrote:
>>> --------- Original Message ---------
>>> Sender : Krzysztof Kozlowski 
>>> Date : 2022-03-28 20:44 (GMT+9)
>>> Title : Re: [PATCH 0/5] Add support for Axis, ARTPEC-8 PCIe driver
>>>
>>> On 28/03/2022 13:29, 이왕석 wrote:
>>>>>  --------- Original Message ---------
>>>>>  Sender : Krzysztof Kozlowski 
>>>>>  Date : 2022-03-28 18:38 (GMT+9)
>>>>>  Title : Re: [PATCH 0/5] Add support for Axis, ARTPEC-8 PCIe driver
>>>>>
>>>>>  On 28/03/2022 11:02, 이왕석 wrote:
>>>>>>>   --------- Original Message ---------
>>>>>>>   Sender : Krzysztof Kozlowski 
>>>>>>>   Date : 2022-03-28 16:12 (GMT+9)
>>>>>>>   Title : Re: [PATCH 0/5] Add support for Axis, ARTPEC-8 PCIe driver
>>>>>>>
>>>>>>>   On 28/03/2022 03:44, 이왕석 wrote:
>>>>>>>>    This series patches include newly PCIe support for Axis ARTPEC-8 SoC.
>>>>>>>>    ARTPEC-8 is the SoC platform of Axis Communications.
>>>>>>>>    PCIe controller driver and phy driver have been newly added.
>>>>>>>>    There is also a new MAINTAINER in the addition of phy driver.
>>>>>>>>    PCIe controller is designed based on Design-Ware PCIe controller IP
>>>>>>>>    and PCIe phy is desinged based on SAMSUNG PHY IP.
>>>>>>>>    It also includes modifications to the Design-Ware controller driver to 
>>>>>>>>    run the 64bit-based ARTPEC-8 PCIe controller driver.
>>>>>>>>    It consists of 6 patches in total.
>>>>>>>>    
>>>>>>>>    This series has been tested on AXIS SW bring-up board 
>>>>>>>>    with ARTPEC-8 chipset.
>>>>>>>
>>>>>>>   You lost mail threading. This makes reading this difficult for us. Plus
>>>>>>>   you sent something non-applicable (patch #2), so please resend.
>>>>>>>
>>>>>>>   Knowing recent Samsung reluctance to extend existing drivers and always
>>>>>>>   duplicate, please provide description/analysis why this driver cannot be
>>>>>>>   combined with existing driver. The answer like: we need several syscon
>>>>>>>   because we do not implement other frameworks (like interconnect) are not
>>>>>>>   valid.
>>>>>>>
>>>>>>>   Best regards,
>>>>>>>   Krzysztof
>>>>>>   
>>>>>>   Hello, Krzysztof
>>>>>>   Thanks for your review.
>>>>>>   
>>>>>>   patch#2 was sent to the wrong format so sent again.
>>>>>>   Sorry for causing confusion.
>>>>>   
>>>>>  The first sending was HTML. Second was broken text, so still not working.
>>>>>
>>>>>  Please resend everything with proper threading.
>>>>  
>>>>  Hello, Krzysztof
>>>>  
>>>>  I sent patch#2 three times.
>>>>  due to the influence of the email system,
>>>>  there was something wrong with the first and second mails.
>>>>  Sorry for causing confusion.
>>>>  Did you receive the third patch i sent you?
>>>
>>> Maybe, I don't know. It's not threaded so it's difficult to find it
>>> among other 100 emails...
>> 
>> I think you also received a normal patch# 2.
>> 
>>>>   
>>>>>>   This patch is specialized in Artpec-8, 
>>>>>>   the SoC Platform of Axis Communication, and is newly applied.
>>>>>>   Since the target SoC platform is different from the driver previously 
>>>>>>   used by Samsung, it is difficult to merge with the existing driver.
>>>>>
>>>>>  Recently I always saw such answers and sometimes it was true, sometimes
>>>>>  not. What is exactly different?
>>>>>
>>>>>  Best regards,
>>>>>  Krzysztof
>>>>  
>>>>  The main reason this patch should be added is that
>>>>  this patch is not the driver applied to exynos platform.
>>>
>>> Still this does not explain why you need separate driver.
>> 
>> PCIe driver of artpec-8 is not available in exynos platform.
>> because the PCIe of artpec and exynos have very different 
>> hardware in SoC design.
>> Not only it is the SoC different, 
>> but the hardware design of PCIe is also different.
>> Therefore, we are using driver's compatible 
>> as axis, artpec8-pcie rather than samsung, artpec8-pcie.
> 
> You keep repeating the same over and over. What is different? Drivers
> can support different devices, I already wrote it. Just because device
> is different does not mean it should have separate driver.
> 
>> 
>>>>  Because the SoC platform is different, 
>>>>  the IP configuration of PCIe is also different.
>>>
>>> What is exactly different? Usually drivers can support IP blocks with
>>> some differences...
>>>
>>>>  We will organize a driver for Artpec-8 platform and 
>>>>  if there is no special reason, maintain this 
>>>>  without adding it from the next series.
>>>
>>> I don't understand this.
>>>
>>>
>>> Best regards,
>>> Krzysztof
>> 
>> Also, as you know,
>> exynos driver is designed according to exynos SoC platform,
>> so both function and variable names start with exynos.
> 
> That's hardly a problem...
> 
>> Compared to the existing exynos driver, 
>> you can see that the structure and type of function are different.
> 
> No, I cannot see it. You coded the driver that way, you can code it in
> other way.
> 
>> For this reason, it is difficult to use the existing exynos driver 
>> for artpec.
> 
> Naming of functions and structures is not making it difficult. That's
> not the reason.
> 
>> Our idea is to register a new PCIe driver for artpec-8 SoC platform 
>> and maintain it in the future.
> 
> We also want to maintain Exynos PCIe driver in the future.
> 
> Best regards,
> Krzysztof

Hi, 
Sorry for delay response.
I have listed some parts that are different from exynos pcie driver.

PHY driver
PHY is different, so register map is also different.
Three reference clock options are available in ARTPEC-8.
  It operates by selecting one clock among XO, IO, and SOC PLL.
  However, the exynos phy driver sets one ref clk though sysreg.
The reset method and type of PHY for initialization are different.
The overall sysreg configuration is different
Artpec-8 requires a separate sequence for phy tuning,
but it does not exist in exynos phy driver.
Artpec-8 requires pcs resources, but exynos phy driver does not exist.

Controller driver
Sub controller is different, so register map is also different.
And it is different handles lane control, link control, PHY clocking,
reset, interrupt control. 
The number and type of clock resources used are different.
The overall sysreg configuration is different

Also artpec-8 is performed in dual mode that supports both RC and EP.
As described above, the PHY and sub ontroller are different
and the regiser map is different.
sysreg is also different. And there are differences such as reset.
The driver will be much more complicated if both hardwares should be
supported in the same driver.
For these reasons, my opinion is that better to create
a phy, controller both driver with a new file.
Please let me know your opinion.

Thank you.

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