linux-kernel - Re: [PATCH] ARM: dts: imx5: Add dts files for USB armory.

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Date:	Mon, 27 Apr 2015 13:48:26 -0700
From:	Vagrant Cascadian <vagrant@...ian.org>
To:	Shawn Guo <shawn.guo@...aro.org>
Cc:	devicetree@...r.kernel.org, Andrej Rosano <andrej@...ersepath.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>,
	Russell King <linux@....linux.org.uk>,
	Sascha Hauer <kernel@...gutronix.de>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: dts: imx5: Add dts files for USB armory.

On 2015-04-27, Shawn Guo wrote:
> On Fri, Mar 27, 2015 at 01:23:00PM -0700, Vagrant Cascadian wrote:
>> Add support for the USB armory board by Inverse Path. This board
>> features a Freescale iMX53 SoC, 512MB RAM, and USB OTG operating in
>> either peripheral or host mode, and 5 GPIO pins.
>> 
>> One .dtb is generated for operating in peripheral mode, and one is
>> generated for operating in host mode.
>
> Is it possible to ask bootloader to patch the dtb instead of maintaining
> a new one for just changing one USB property?

It does appear to be possible with u-boot:

  load mmc 0:1 $fdt_addr_r $fdtfile
  fdt addr $fdt_addr_r
  fdt set /soc/aips@...00000/usb@...80000 dr_mode host

Since the user would have to manually select the appropriate .dtb
anyways, it may be reasonable to drop the host_mode.dtb and rely on the
u-boot to tweak the fdt on boot to switch between usb modes.

It is considerably more complicated than setting the fdtfile variable to
the desired .dtb, as various out-of-the box boot scripts will load the
.dtb file defined in the fdtfile variable, overwriting any changes made
with "fdt set".

Given the additional complication in boot scripts, my preference would
be to ship both .dtb files...

Thanks for the time and consideration!

live well,
  vagrant

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