linux-kernel - Re: Query regarding the use of pcie-designware-plat.c file

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Date:   Tue, 15 Jun 2021 08:58:26 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     Thierry Reding <treding@...dia.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>
CC:     Gustavo Pimentel <Gustavo.Pimentel@...opsys.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "amurray@...goodpenguin.co.uk" <amurray@...goodpenguin.co.uk>,
        "jingoohan1@...il.com" <jingoohan1@...il.com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Krishna Thota <kthota@...dia.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Query regarding the use of pcie-designware-plat.c file

Bjorn / Lorenzo,
Could you please comment on the options proposed by Thierry?

- Vidya Sagar

On 6/9/2021 3:19 PM, Thierry Reding wrote:
> On Wed, Jun 09, 2021 at 10:56:48AM +0530, Vidya Sagar wrote:
>>
>>
>> On 6/9/2021 2:47 AM, Gustavo Pimentel wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>
>>> Hi Vidya,
>>>
>>> The pcie-designware-plat.c is the driver for the Synopsys PCIe RC IP
>>> prototype.
>> Thanks for the info Gustavo.
>> But, I don't see any DT file having only "snps,dw-pcie" compatibility
>> string. All the DT files that have "snps,dw-pci" compatibility string also
>> have their platform specific compatibility string and their respective host
>> controller drivers. Also, it is the platform specific compatibility string
>> that is used for binding purpose with their respective drivers and not the
>> "snps,dw-pcie". So, wondering when will pcie-designware-plat.c be used as
>> there is not DT file which has only "snps,dw-pcie" as the compatibility
>> string.
> 
> Sounds to me like we have two options:
> 
>    1. If there's indeed real hardware that's identified by the existing
>       "snps,dw-pcie" compatible string, then it's wrong for other devices
>       to list that in their compatible string because they are likely not
>       compatible with that (i.e. they might be from a register point of
>       view, but at least from an integration point of view they usually
>       differ).
> 
>    2. If "snps,dw-pcie" is meant to describe the fact that these are all
>       based off the same IP but may be differently integrated, then there
>       should be no driver matching on that compatible string.
> 
> Option 2 is not very robust because somebody could easily add a matching
> driver at some point in the future. Also, if we don't match on a
> compatible string there's not a lot of use in listing it in DT in the
> first place.
> 
> So I think option 1 would be preferred.
> 
> Thierry
>