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

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Message-ID: <20211025211236.GA31293@bhelgaas>
Date:   Mon, 25 Oct 2021 16:12:36 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sergio Paracuellos <sergio.paracuellos@...il.com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh+dt@...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 11:13:39AM +0200, Sergio Paracuellos wrote:
> 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

OK, for now I left my rework as-is:

  - changed CONFIG_PCI_MT7621 to CONFIG_PCIE_MT7621
  - renamed mediatek,mt7621-pci.yaml to mediatek,mt7621-pcie.yaml
  - renamed pci-mt7621.c to pcie-mt7621.c
  - kept DT compatible string "mediatek,mt7621-pci" in .yaml and .c

I reason that the Kconfig and filename changes only affect people
building kernels or DTs, but a compatible string change would force a
DT update to be synchronized with a kernel update.

Happy to change this if necessary.

Bjorn