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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Mateusz Holenko <mholenko@antmicro.com>
Cc: Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>, Jiri Slaby <jslaby@suse.com>,
	devicetree@vger.kernel.org,
	"open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
	Stafford Horne <shorne@gmail.com>,
	Karol Gugala <kgugala@antmicro.com>,
	Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	"Paul E. McKenney" <paulmck@linux.ibm.com>,
	Filip Kokosinski <fkokosinski@internships.antmicro.com>,
	Joel Stanley <joel@jms.id.au>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Maxime Ripard <mripard@kernel.org>,
	Shawn Guo <shawnguo@kernel.org>, Heiko Stuebner <heiko@sntech.de>,
	Sam Ravnborg <sam@ravnborg.org>, Icenowy Zheng <icenowy@aosc.io>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/4] litex: add common LiteX header
Date: Tue, 26 Nov 2019 10:19:26 +0100	[thread overview]
Message-ID: <20191126091926.GB1372654@kroah.com> (raw)
In-Reply-To: <CAPk366QgcOYPZJXM46o3Gn8ksFYYoNwJvnunUe7y0aLNgJuSRg@mail.gmail.com>

On Tue, Nov 26, 2019 at 10:02:18AM +0100, Mateusz Holenko wrote:
> śr., 20 lis 2019 o 20:26 Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> napisał(a):
> >
> > On Wed, Oct 23, 2019 at 11:47:04AM +0200, Mateusz Holenko wrote:
> > > +#ifdef __LITTLE_ENDIAN
> > > +# define LITEX_READ_REG(addr)                  ioread32(addr)
> > > +# define LITEX_READ_REG_OFF(addr, off)         ioread32(addr + off)
> > > +# define LITEX_WRITE_REG(val, addr)            iowrite32(val, addr)
> > > +# define LITEX_WRITE_REG_OFF(val, addr, off)   iowrite32(val, addr + off)
> > > +#else
> > > +# define LITEX_READ_REG(addr)                  ioread32be(addr)
> > > +# define LITEX_READ_REG_OFF(addr, off)         ioread32be(addr + off)
> > > +# define LITEX_WRITE_REG(val, addr)            iowrite32be(val, addr)
> > > +# define LITEX_WRITE_REG_OFF(val, addr, off)   iowrite32be(val, addr + off)
> > > +#endif
> >
> > I just noticed this.
> >
> > Ick, this is not good.  You will run into problems in the future with
> > this, I can guarantee it.  What about systems where the CPU is one
> > endian and the hardware in the other?  It will happen trust us.
> 
> As mentioned in the previous comment, LiteX CSRs are guaranteed to be
> always little-endian - this includes configurations with both
> big-endian and little-endian CPUs.

What enforces that guarantee?

> The aim of including the ifdef section was exactly to target situation
> where endianness is different for CPU and devices. As such this
> approach *should* work.

"should" :)

We have seen it happen all the time that some hardware team hooks this
up backwards, no matter what the "spec" required.  So be careful here.

good luck!

greg k-h

  reply	other threads:[~2019-11-26  9:19 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-23  9:46 [PATCH v2 0/4] LiteUART serial driver Mateusz Holenko
2019-10-23  9:46 ` [PATCH v2 1/4] dt-bindings: vendor: add vendor prefix for LiteX Mateusz Holenko
2019-10-25 23:36   ` Rob Herring
2019-10-23  9:47 ` [PATCH v2 2/4] litex: add common LiteX header Mateusz Holenko
2019-10-26  0:03   ` Rob Herring
2019-11-07  9:27     ` Mateusz Holenko
2019-11-20 17:23   ` Gabriel L. Somlo
2019-11-20 19:26   ` Greg Kroah-Hartman
2019-11-26  9:02     ` Mateusz Holenko
2019-11-26  9:19       ` Greg Kroah-Hartman [this message]
2019-11-29 15:39         ` Mateusz Holenko
2019-10-23  9:47 ` [PATCH v2 3/4] dt-bindings: serial: document LiteUART bindings Mateusz Holenko
2019-10-26  0:14   ` Rob Herring
2019-10-23  9:47 ` [PATCH v2 4/4] drivers/tty/serial: add LiteUART driver Mateusz Holenko
2019-10-26  0:13   ` Rob Herring
2019-11-07  9:33     ` Mateusz Holenko

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