linux-kernel - Re: [PATCH-RFC 6/7] drivers: of: ifdef out cmdline section

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Date:	Wed, 14 Oct 2015 12:57:16 -0500
From:	Rob Herring <robh@...nel.org>
To:	Daniel Walker <danielwa@...co.com>
Cc:	Rob Herring <robh@...nel.org>, Daniel Walker <dwalker@...o99.com>,
	xe-kernel@...ernal.cisco.com,
	Frank Rowand <frowand.list@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH-RFC 6/7] drivers: of: ifdef out cmdline section

On Wed, Oct 14, 2015 at 9:48 AM, Daniel Walker <danielwa@...co.com> wrote:
>
>
> There's one last little wrinkle .. In the current setup the defconfig
> CONFIG_CMDLINE="" is used as a default in case the device tree has nothing
> in it. In my changes, there is no identical functionality. The only similar
> thing I have is the the CONFIG_CMDLINE_APPEND="" . The main difference is
> that in the current implementation CONFIG_CMDLINE="" doesn't get added at
> all if there is a device tree bootargs, but with my implementation this line
> would be added unconditionally. It would represent a subtle change where
> people would have to add into the DT bootargs something to override what
> might be in the default command line.

So CMDLINE_EXTEND would be equivalent to your version, but it looks
like CMDLINE_EXTEND is not used in the DT case. Perhaps you can add
the option? You already have OVERRIDE which is equivalent to FORCE.


> For example,
>
> if a config has CONFIG_CMDLINE_APPEND="debug" then they would have to add a
> "loglevel=7" into the DT bootargs to get back to normal. I wouldn't think
> people would want "debug" as the default, but oddly enough some of the
> configs do have this. Some of them also have default ip address setting,
> nfsroot= settings, and loglevel= settings.

Or they would have to remove the kernel default from their config.
That might be acceptable. You could have a case where you have 1
kernel binary and 2 different bootloaders where you expect the
bootloader's cmdline used in one case and the kernel's in the other.
Seems unlikely, but it would be an ABI break.

I would not judge people's choices of defaults making sense...

> What are your thoughts on this ? I think using the append type default makes
> more sense because it's actually setting up global defaults. The current
> complete replacement scheme seems to set the stage for people to make an
> entirely custom default for a single development machine, which IMO doesn't
> make sense. However, I'm not sure what the intent is with the current setup.

People will want a path to support up to the current 3 options (use
bootloader's cmdline, append bootloader cmdline to default, and force
kernel default) and you have to assume changing bootloader is not an
option.

Rob

>
> Daniel
> --
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