linux-kernel - Re: [PATCH v8 07/10] i3c: master: Add driver for Cadence IP

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Date:   Mon, 8 Oct 2018 12:36:44 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     Wolfram Sang <wsa@...-dreams.de>,
        Linux I2C <linux-i2c@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        gregkh <gregkh@...uxfoundation.org>,
        Przemyslaw Sroka <psroka@...ence.com>,
        Arkadiusz Golec <agolec@...ence.com>,
        Alan Douglas <adouglas@...ence.com>,
        Bartosz Folta <bfolta@...ence.com>,
        Damian Kos <dkos@...ence.com>,
        Alicja Jurasik-Urbaniak <alicja@...ence.com>,
        Cyprian Wronka <cwronka@...ence.com>,
        Suresh Punnoose <sureshp@...ence.com>,
        Rafal Ciepiela <rafalc@...ence.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Nishanth Menon <nm@...com>, Rob Herring <robh+dt@...nel.org>,
        Pawel Moll <pawel.moll@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ian Campbell <ijc+devicetree@...lion.org.uk>,
        Kumar Gala <galak@...eaurora.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Vitor Soares <Vitor.Soares@...opsys.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Xiang Lin <Xiang.Lin@...aptics.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Sekhar Nori <nsekhar@...com>,
        Przemyslaw Gaj <pgaj@...ence.com>,
        Peter Rosin <peda@...ntia.se>, mshettel@...eaurora.org,
        swboyd@...omium.org
Subject: Re: [PATCH v8 07/10] i3c: master: Add driver for Cadence IP

On Mon, Oct 8, 2018 at 12:21 PM Boris Brezillon
<boris.brezillon@...tlin.com> wrote:
>
> On Mon, 8 Oct 2018 12:06:30 +0200
> Arnd Bergmann <arnd@...db.de> wrote:
>
> > On Wed, Oct 3, 2018 at 3:22 PM Boris Brezillon
> > <boris.brezillon@...tlin.com> wrote:
> > >
> > > Add a driver for Cadence I3C master IP.
> > >
> > > Signed-off-by: Boris Brezillon <boris.brezillon@...tlin.com>
> > > ---
> >
> > > Changes in v7:
> > > - Fix readsl/writesl() usage
> > > - Add a depends on ARM || ARM64 || XTENSA to forbid selection of this
> > >   driver on platforms that are not implementing readsl/writesl
> >
> > Most architectures include asm-generic/io.h, which contains a generic
> > implementation of readsl(). Maybe that #ifdef could be extended here?
> > I remember discussing this with you not so long ago, which led to
> > commit 0bbf47eab469 ("ia64: use asm-generic/io.h"). Do we have
> > a list of architectures that don't include asm-generic/io.h? Maybe
> > the 'depends on' could be for the set of architectures that fail here.
>
> Well, we started patching 2 archs (ia64 and sparc) based on kbuild
> robots failure report, and then I received other reports (still from
> kbuild robots) long after the initial ones. I can't tell for sure which
> archs are not implementing those functions, hence the conservative
> approach taken here.

I think it's a fairly safe assumption that architectures which include
asm-generic/io.h will be fine here. If one of them is broken, that
can be fixed individually. Looking at the ones that don't include this
file:

grep -L asm-generic/io.h arch/*/include/asm/io*.h
arch/alpha/include/asm/io.h        # missing readsl
arch/hexagon/include/asm/io.h   # has its own readsl
arch/mips/include/asm/io.h         # missing readsl (but used from ide.h?)
arch/parisc/include/asm/io.h       # missing readsl
arch/powerpc/include/asm/io.h   # has its own readsl
arch/sh/include/asm/io.h             # has its own readsl
arch/sparc/include/asm/io.h        # has its own readsl

Based on this, I would try what happens on mips, and make it depend
on !(ALPHA || PARISC)

Another option is to just use ioread32_rep(), which should be
available everywhere and has almost the same behavior as
readsl(). The only difference is that on architectures like x86
it takes a few extra cycles to look at the address.

        Arnd