linux-kernel - Re: [PATCH v4 3/5] PCI: axis: Add ARTPEC-8 PCIe controller driver

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Date:   Fri, 22 Jul 2022 19:36:01 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     wangseok.lee@...sung.com,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzk+dt@...nel.org" <krzk+dt@...nel.org>,
        "kishon@...com" <kishon@...com>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jesper.nilsson@...s.com" <jesper.nilsson@...s.com>,
        "lars.persson@...s.com" <lars.persson@...s.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-phy@...ts.infradead.org" <linux-phy@...ts.infradead.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "kw@...ux.com" <kw@...ux.com>,
        "linux-arm-kernel@...s.com" <linux-arm-kernel@...s.com>,
        "kernel@...s.com" <kernel@...s.com>,
        Moon-Ki Jun <moonki.jun@...sung.com>,
        Sang Min Kim <hypmean.kim@...sung.com>,
        Dongjin Yang <dj76.yang@...sung.com>,
        Yeeun Kim <yeeun119.kim@...sung.com>
Subject: Re: [PATCH v4 3/5] PCI: axis: Add ARTPEC-8 PCIe controller driver

On 21/07/2022 22:58, Bjorn Helgaas wrote:
> On Thu, Jul 21, 2022 at 11:04:00AM +0200, Krzysztof Kozlowski wrote:
>> On 20/07/2022 08:01, Wangseok Lee wrote:
>>> Add support Axis, ARTPEC-8 SoC. ARTPEC-8 is the SoC platform of Axis
>>> Communications. This is based on arm64 and support GEN4 & 2lane. This
>>> PCIe controller is based on DesignWare Hardware core and uses DesignWare
>>> core functions to implement the driver. "pcie-artpec6. c" supports artpec6
>>> and artpec7 H/W. artpec8 can not be expanded because H/W configuration is
>>> completely different from artpec6/7. PHY and sub controller are different.
>>>
>>> Signed-off-by: Wangseok Lee <wangseok.lee@...sung.com>
>>> Signed-off-by: Jaeho Cho <jaeho79.cho@...sung.com>
>>> ---
>>> v3->v4 :
>>> -Remove unnecessary enum type
>>> -Fix indentation
>>>
>>
>> Thanks for the changes. This starts to look good, however I am not going
>> to ack it. This is also not a strong NAK, as I would respect Bjorn and
>> other maintainers decision.
>>
>> I don't like the approach of creating only Artpec-8 specific driver.
>> Samsung heavily reuses its block in all Exynos devices. Now it re-uses
>> them for other designs as well. Therefore, even if merging with existing
>> Exynos PCIe driver is not feasible (we had such discussions), I expect
>> this to cover all Samsung Foundry PCIe devices. From all current designs
>> up to future licensed blocks, including some new Samsung Exynos SoC. Or
>> at least be ready for it.
> 
> I would certainly prefer fewer drivers but I don't know enough about
> the underlying IP and the places it's integrated to to know what's
> practical.  The only way I could figure that out would be by manually
> comparing the drivers for similarity.  I assume/expect all driver
> authors are doing that.

Merging with existing Exynos PCIe driver (and phy) might be indeed
tricky, as existing one does not support that much as here. However I
really expect that all current designs from Samsung - Exynos SoC, Artpec
and for other customers - have very similar PCIe thus this should be a
generic, new generation Samsung PCIe driver. If designed that way, also
the naming should be back Samsung specific, no Axis/Artpec.

Best regards,
Krzysztof