linux-kernel - Re: [PATCH v3 00/3] MIPS: SGI-IP27 rework part2

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Message-Id: <20190507174820.381fd56f678609416fd8b617@suse.de>
Date:   Tue, 7 May 2019 17:48:20 +0200
From:   Thomas Bogendoerfer <tbogendoerfer@...e.de>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v3 00/3] MIPS: SGI-IP27 rework part2

On Tue, 7 May 2019 16:31:17 +0100
Lorenzo Pieralisi <lorenzo.pieralisi@....com> wrote:

> On Thu, Apr 18, 2019 at 03:57:26PM -0500, Bjorn Helgaas wrote:
> > Hi Thomas,
> > 
> > On Tue, Mar 19, 2019 at 04:47:49PM +0100, Thomas Bogendoerfer wrote:
> > > SGI IP27 (Origin/Onyx2) and SGI IP30 (Octane) have a similair
> > > architecture and share some hardware (ioc3/bridge). To share
> > > the software parts this patchset reworks SGI IP27 interrupt
> > > and pci bridge code. By using features Linux gained during the
> > > many years since SGI IP27 code was integrated this even results
> > > in code reduction and IMHO cleaner code.
> > > 
> > > Tests have been done on a two module O200 (4 CPUs) and an
> > > Origin 2000 (8 CPUs).
> > 
> > Thanks for doing all this work!  It seems like it basically converts
> > some of the SGI PCI code to the structure typical of current host
> > controller drivers and moves it to drivers/pci/controller, which all
> > seems great to me.
> 
> I had a look and the code is really, really MIPS specific, actually
> I would be interested in understanding how many platforms it supports,
> it is not even FW configurable.

it's MIPS only and used in basically 3 different SGI platforms.

> With hard-coded resources, <asm/...> includes in driver code and MIPS
> specific kludges even if it does reuse some APIs shared with controller
> drivers I am not 100% certain that moving it to drivers/pci/controller
> buys us anything, this is really arch specific code, however we slice
> it.

hmm, I thought the idea of having one drivers/pci/controller directory
is to have all of them in one place.

> The line between what stays in arch and what goes to
> drivers/pci/controller is thin but this code is definitely more on the
> arch side IMHO.

what makes the xgene driver different from the xtalk-bridge driver ? Ok
it used DT, but it's still just for a specific type of SOCs from one
vendor, isn't it ?

> I do not question Thomas' effort, which I appreciate, I question
> the end result and its usefulness, this series is even increasing
> lines of kernel code, I would like to see the benefits.

the move from arch/mips/pci to drivers/pci/controller increases lines of
code by two lines. The whole patchset adds 155 lines, but also adds
functionality to be able to use the driver with different platforms.

Anyway I can live with not moving to drivers/pci/controller if you don't
like it there.

Thomas.

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