linux-kernel - Re: [PATCH v3 0/3] PCI: mt7621: Add MediaTek MT7621 PCIe host controller driver

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Message-ID: <CAMhs-H90rD8aHJ+txDzFZ62Ej9_TY=BZMT+1058d=Pm_LfYwPA@mail.gmail.com>
Date:   Fri, 22 Oct 2021 11:13:39 +0200
From:   Sergio Paracuellos <sergio.paracuellos@...il.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        John Crispin <john@...ozen.org>, NeilBrown <neil@...wn.name>,
        Greg KH <gregkh@...uxfoundation.org>,
        linux-staging@...ts.linux.dev,
        Matthias Brugger <matthias.bgg@...il.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v3 0/3] PCI: mt7621: Add MediaTek MT7621 PCIe host
 controller driver

On Fri, Oct 22, 2021 at 10:35 AM Lorenzo Pieralisi
<lorenzo.pieralisi@....com> wrote:
>
> On Thu, Oct 21, 2021 at 09:23:35PM +0200, Sergio Paracuellos wrote:
> > On Thu, Oct 21, 2021 at 8:11 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
> > >
> > > On Thu, Oct 21, 2021 at 07:27:21PM +0200, Sergio Paracuellos wrote:
> > > > On Thu, Oct 21, 2021 at 5:52 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
> > > > > Since this is a PCIe (not conventional PCI) controller, I vote for
> > > > > renaming these from:
> > > > >
> > > > >   PCI_MT7621
> > > > >   Documentation/devicetree/bindings/pci/mediatek,mt7621-pci.yaml
> > > > >   drivers/pci/controller/pci-mt7621.c
> > > > >
> > > > > to:
> > > > >
> > > > >   PCIE_MT7621
> > > > >   Documentation/devicetree/bindings/pci/mediatek,mt7621-pcie.yaml
> > > > >   drivers/pci/controller/pcie-mt7621.c
> > > > >
> > > > > We have a mix of these, with many of the early PCIe drivers being
> > > > > named "pci", but I think that was my mistake and there's no reason to
> > > > > continue it.
> > > >
> > > > I see.
> > > >
> > > > >
> > > > > I can do this locally unless somebody objects.
> > > >
> > > > I have no problem at all. Only one question. Do you mean to change
> > > > compatible string also, or only the name of the file? Let me know if I
> > > > have to do anything.
> > >
> > > I didn't change the compatible string, to avoid a DT incompatibility.
> > > But I *did* change the Kconfig symbol to PCIE_MT7621, which could
> > > require changes to out-of-tree .configs.  I'm open to suggestions
> > > either way for both things.
> >
> > IMHO, I do think we should not worry about out-of-tree stuff at all.
>
> For Kconfig I tend to agree. For DT I see some "bindings" in the staging
> tree are being deleted and published as official DT bindings with this
> patchset but I believe we still have to keep the compatible string
> backward compatibility regardless because there may be firmware out
> there using it.

The bindings txt file removed in staging with this patchset was also
added by me three years ago[0], and has been changing until the YAML
bindings are reviewed by Rob and driver updated accordly in this
patchset.
OpenWRT maintains its own file[1] which I don't know is updated or not
according to the one in staging which I am pretending to properly
mainline for 5.17. But yes, I agree there might be firmware out there
using current compatible string.

[0]: Commit 5451e22618b8 ("staging: mt7621-pci: dt-bindings: add dt
bindings for mt7621 pcie controller")
[1]: https://github.com/openwrt/openwrt/blob/master/target/linux/ramips/dts/mt7621.dtsi

Best regards,
    Sergio Paracuellos
>
> Rob, what's the standard policy that should be used in this case ?
>
> Thanks,
> Lorenzo
>
> > If the correct way to define the Kconfig symbol or the compatible
> > string is to change them, just do that. MT7621 SoC is extensively used
> > by openWRT community. As far as I have seen until now, the way of
> > doing things there is to take the latest long term kernel (now they
> > are using 5.4 as stable and 5.10 as testing kernel), apply a bunch of
> > patches they have and do a complete build of both kernel, device tree
> > and rootfs. So I guess it is not a big problem if we also change
> > compatible string since when an update is performed for a device all
> > of the stuff is just replaced. Maybe I am wrong and John has a
> > different opinion... John, any comments on this?
> >
> > Best regards,
> >     Sergio Paracuellos