Date: Fri, 23 Aug 2013 16:11:52 +0800
From: Shawn Guo <shawn.guo@linaro.org>
To: Dong Aisheng <b29396@freescale.com>
CC: Grant Likely <grant.likely@linaro.org>, Rob Landley <rob@landley.net>,
        <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Rob Herring <rob.herring@calxeda.com>,
        "linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 0/3] of: add update device node status via cmdline feature
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On Fri, Aug 23, 2013 at 03:51:07PM +0800, Shawn Guo wrote:
> The device tree mailing list is changed to devicetree@vger.kernel.org.
> 
> On Fri, Aug 23, 2013 at 03:09:08PM +0800, Dong Aisheng wrote:
> > I tried the uboot way with fdt command to change the node status, it can work.
> > However, it seems using fdt command is much complicated than the way i did with kernel
> > command line and it also does not support enable/disable multi nodes at the same time.
> > e.g, in order to enable ecspi1 and uart3 and disable gpmi:
> > with uboot fdt command:
> > U-Boot > fdt addr ${dtbaddr}
> > U-Boot > fdt set /soc/aips-bus@02000000/spba-bus@02000000/ecspi@02008000 status "okay"
> > U-Boot > fdt set /soc/aips-bus@02100000/serial@021e8000 status "okay"
> > U-Boot > fdt set /soc/gpmi-nand@00112000 status "disabled"
> 
> Oh, you can use the U-Boot environment and scripting function to make
> it even easier than your kernel cmdline approach to use.
> 
> > with kernel cmdline:
> > fdt.enable=ecspi@02008000,serial@021e8000 fdt.disable=gpmi-nand@00112000
> > So from the using perspective, kernel command line is much more simple and easy than uboot.
> 
> NAK.
> 
> It's not about simple or easy.  The approach completely defects the

s/defects/defeats

Shawn

> point of the whole device tree project - moving stuff that kernel does
> not care out of kernel.  Choosing device from mutually exclusive ones
> (due to pin conflict of board design) should NOT be something that
> kernel cares.
> 
> Kernel gets device tree blob from firmware/bootloader and instantiates
> drivers for devices found in device tree.  That's all what kernel should
> do, nothing more.  Asking kernel to manipulate the device availability
> property in device tree is plainly wrong to me.
> 
> If your board is designed with so many pin conflicts between devices,
> you have to do whatever you can do to get the decision made in device
> tree blob, before it gets passed to kernel.  Kernel does NOT care about
> that decision making.

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