linux-kernel - Re: [RFC PATCH v2 2/6] bus/cdx: add the cdx bus driver

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Message-ID: <20220824233122.GA4068@nvidia.com>
Date:   Wed, 24 Aug 2022 20:31:22 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     "Gupta, Nipun" <Nipun.Gupta@....com>,
        Robin Murphy <robin.murphy@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "Gupta, Puneet (DCG-ENG)" <puneet.gupta@....com>,
        "song.bao.hua@...ilicon.com" <song.bao.hua@...ilicon.com>,
        "mchehab+huawei@...nel.org" <mchehab+huawei@...nel.org>,
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        "mani@...nel.org" <mani@...nel.org>,
        "yishaih@...dia.com" <yishaih@...dia.com>,
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        "okaya@...nel.org" <okaya@...nel.org>,
        "Anand, Harpreet" <harpreet.anand@....com>,
        "Agarwal, Nikhil" <nikhil.agarwal@....com>,
        "Simek, Michal" <michal.simek@....com>,
        "git (AMD-Xilinx)" <git@....com>
Subject: Re: [RFC PATCH v2 2/6] bus/cdx: add the cdx bus driver

On Wed, Aug 24, 2022 at 02:11:48PM +0200, Greg KH wrote:
> > We can share the RFC in case you are interested in looking at code flow
> > using the of_dynamic approach.
> 
> Please no more abuse of the platform device.

Last time this came up there was some disagreement from the ARM folks,
they were not keen on having xx_drivers added all over the place to
support the same OF/DT devices just discovered in a different way. It is
why ACPI is mapped to platform_device even in some cases.

I think if you push them down this path they will get resistance to
get the needed additional xx_drivers into the needed places.

> If your device can be discovered by scanning a bus, it is not a platform
> device.

A DT fragment loaded during boot binds a driver using a
platform_driver, why should a DT fragment loaded post-boot bind using
an XX_driver and further why should the CDX way of getting the DT
raise to such importantance that it gets its own cdx_driver ?

In the end the driver does not care about how the DT was loaded.
None of these things are on a discoverable bus in any sense like PCI
or otherwise. They are devices described by a DT fragement and they
take all their parameters from that chunk of DT.

How the DT was loaded into the system is not a useful distinction that
raises the level of needing an entire new set of xx_driver structs all
over the tree, IMHO.

Jason