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

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Date:   Tue, 26 Oct 2021 07:49:16 +0200
From:   Sergio Paracuellos <sergio.paracuellos@...il.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
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 Mon, Oct 25, 2021 at 11:12 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> 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.

This is all ok for me, Bjorn. Thanks for doing this. I guess even if
we don't force people to a DT update to synchronize things, since
bindings have been changed until they have been approved, I guess most
people must upgrade from early not approved DT early versions in any
case. But in any case I guess that maintaining the compatible string
is the safest thing to do.

>
> Happy to change this if necessary.

Best regards,
    Sergio Paracuellos

>
> Bjorn