linux-kernel - Re: [PATCH 0/4] MIPS: ralink: pci: driver for Pcie controller in MT7621 SoCs

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Message-ID: <20210604194328.GA2230062@bjorn-Precision-5520>
Date:   Fri, 4 Jun 2021 14:43:28 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Pali Rohár <pali@...nel.org>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Sergio Paracuellos <sergio.paracuellos@...il.com>,
        lorenzo.pieralisi@....com,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        John Crispin <john@...ozen.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        linux-staging@...ts.linux.dev,
        Greg KH <gregkh@...uxfoundation.org>,
        NeilBrown <neil@...wn.name>,
        Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH 0/4] MIPS: ralink: pci: driver for Pcie controller in
 MT7621 SoCs

On Mon, May 31, 2021 at 03:18:45PM +0200, Pali Rohár wrote:
> On Friday 21 May 2021 12:23:38 Thomas Bogendoerfer wrote:
> > On Wed, May 19, 2021 at 11:18:36PM +0200, Sergio Paracuellos wrote:
> > > On Wed, May 19, 2021 at 10:36 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
> > > > But most of the similar drivers are in drivers/pci/controller/, where
> > > > I think it's easier to keep them up to date with changes in the PCI
> > > > core.  Have you considered putting this one there?
> > > 
> > > Most pci drivers in 'arch/mips/pci' are still using PCI_LEGACY stuff.
> > > In contrast mt7621-pci is using current pci generic apis but even most
> > > of the code is generic enough, there is one remaining thing which
> > > depends on mips architecture which is the iocu region configuration
> > > which must be done in the driver itself. This is the only reason to
> > > move this driver into 'arch/mips/pci' instead of
> > > 'drivers/pci/controller/'. So... I am all ears to listen to
> > > suggestions for the proper place for this driver. Thomas, do you have
> > > any thoughts on this?
> > 
> > I tried to put a pci-xtalk driver into drivers/pci/controller, but
> > Lorenzo didn't want it there for being MIPS and not DT based. So this
> > one is DT based, but still MIPS. I'm perfectly fine putting this
> > driver into drivers/pci/controller/
> 
> In my personal opinion this driver could go into drivers/pci/controller/

I'm not sure exactly what "PCI_LEGACY" above refers to.

I don't see any direct #includes of arch/mips in the driver.  I do see
that it uses mips_cps_numiocu(), which is certainly MIPS-specific.

But we do have some things in drivers/pci/controller/ that only build
on certain arches, enforced mostly by Kconfig rules, so I think you
could do that.  We try to make so things can at least be *compiled* on
any arch, but I know that's not always possible.

So I think it would be useful to put this in drivers/pci/controller/
somewhere because it will make it easier to see common patterns and
refactoring opportunities.

Bjorn