linux-kernel - Re: [PATCH v5] bus: uniphier-system-bus: add UniPhier System Bus driver

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Message-ID: <20151222192252.GO30172@localhost>
Date:	Tue, 22 Dec 2015 11:22:52 -0800
From:	Olof Johansson <olof@...om.net>
To:	Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:	arm@...nel.org, Mark Rutland <mark.rutland@....com>, arnd@...db.de,
	devicetree@...r.kernel.org, Kumar Gala <galak@...eaurora.org>,
	linux-kernel@...r.kernel.org,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5] bus: uniphier-system-bus: add UniPhier System Bus
 driver

On Wed, Dec 09, 2015 at 03:52:59PM +0900, Masahiro Yamada wrote:
> The UniPhier System Bus is an external bus that connects on-board
> devices to the UniPhier SoC.  Each bank (chip select) is dynamically
> mapped to the CPU-viewed address base via the bus controller.  The
> bus controller must be configured before any access to the bus.
> 
> This driver parses the "ranges" property of the System Bus node and
> initialized the bus controller.  After the bus becomes ready, devices
> below it are populated.
> 
> Note:
> Each bank can be mapped anywhere in the supported address space;
> there is nothing preventing us from assigning bank 0 on 0x42000000,
> 0x43000000, or anywhere as long as such region is not used by others.
> So, the "ranges" is just one possible software configuration, which
> does not seem to fit in device tree because device tree is a hardware
> description language.  However, of_translate_address() requires
> "ranges" in every bus node between CPUs and device mapped on the CPU
> address space.  In other words, "ranges" properties must be statically
> defined in device tree.  After some discussion, I decided the dynamic
> address reassignment by the driver is too bothersome.  Instead, the
> device tree should provide a reasonable translation setup that the OS
> can rely on.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> Acked-by: Rob Herring <robh@...nel.org>
> Acked-by: Arnd Bergmann <arnd@...db.de>

Thanks, applied to next/drivers.


-Olof

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